Blood glucose level sensing device

Abstract

A blood glucose level sensing device for non-invasive blood glucose level measurement of a subject is disclosed. The device comprises: a digit-depth unit configured to measure or receive a depth of a digit of the subject; a measurement light generation element configured to direct measurement light through the digit; and a light-transmission measurement unit configured to measure a transmission index representing the proportion of the measurement light transmitted through the digit. The device also has a digit characteristic parameter unit configured to receive one or more digit characteristic parameters indicative of: a skin tone of the digit; a nail texture of the digit; a nail thickness of the digit; a nail length of the digit; and a nail polish status of the digit. The device is configured to determine a blood glucose level measurement based on the transmission index, the depth of the digit and at least one of the digit characteristic parameters. Also disclosed is a method of non-invasively determining a blood glucose level of a subject via a digit of the subject.

Description

[0001] Blood Glucose Level Sensing Device

[0002] Field of the Invention

[0003] The present invention relates to a blood glucose level sensing device for non-invasive blood glucose measurement, a blood glucose monitoring system and a method of non-invasively measuring a blood glucose value of a patient via a digit of a subject.

[0004] Background

[0005] The term diabetes mellitus describes a metabolic disorder having a multi-faceted etiology, characterized by chronic hyperglycemia with disturbances of carbohydrate, fat, and protein metabolism resulting from defects in insulin secretion, insulin action, or both. Although the fatality rate of diabetes has fallen substantially and the acute symptoms of diabetes can now be efficiently alleviated following the maturation of targeted medical treatment, its long-term chronic damage has severe impacts on patients’ lives, which include dysfunction or failure of different organs, especially the eyes, kidneys, nerves, heart, and blood vessel hyperglycemia. In the 21st century, diabetes mellitus is becoming a serious health concern and has been declared a global epidemic by the World Health Organization (WHO) due to its rapidly increasing incidence. The present increase in the number of diabetics worldwide was historically underestimated. The number of diabetics, as estimated by the WHO in 2004, was expected to increase from 171 million in 2000 to 366 million by 2030. However, the International Diabetes Federation recently estimated that the number of diabetics in 2011 was over 366 million, and this figure is expected to increase up to 552 million by 2030. As the most populous country, China ranks number one in diabetics, with an estimate of 109.6 million adults with diabetes. Over the past three decades, the prevalence of diabetes in China has dramatically increased. The prevalence of diabetes was reported to be less than 1% in 1980, 5.5% in 2001 , 9.7% in 2008, and 10.9% in 2013. Factors such as obesity, aging, diet, and physical activity have replaced genetic factors in recent years, becoming the most common factors that cause diabetes. Simultaneously, the expected expenditure on diabetes treatment worldwide is substantial. Expenditure on the prevention, diagnosis, management, and treatment of diabetes is over $ 376 billion per annum in the US. This figure is expected to rise to $ 490 billion by the end of 2030.

[0006] Therefore, controlling the increase in the number of diabetics has become a major medical problem in the 21stcentury.

[0007] Blood glucose level (BGL) monitoring plays a significant role in both the diagnosis and the management of diabetes. For decades, the diagnosis of diabetes has been based on glucose criteria, either the fasting plasma glucose (FPG) or the 75-g oral glucose tolerance test (OGTT). The diagnostic cut point of BGL presently used worldwide is 126 mg / dl (7.0 mmol / l), which was set in 1997 by the Expert Committee on The Diagnosis and Classification of Diabetes Mellitus. Meanwhile, as the most crucial index for people with diabetes, real-time BGL can also objectively reflect whether diabetes is under control or not for a person. Recent research has verified that people with diabetes who do frequent and regular monitoring of BGL are less likely to have complications. The severity of diabetes among these frequently and regularly monitoring patients is also lower than the average diabetic.

[0008] The present invention has been devised in light of the above considerations.

[0009] Summary of the Invention

[0010] The present invention relates to a device that determines the blood glucose level of a subject using multiple parameters.

[0011] In a first aspect of the invention, there is provided a blood glucose level sensing device for non-invasive blood glucose level measurement of a subject, the device comprising: a digit-depth unit configured to measure or receive a depth of a digit of the subject; a measurement light generation element configured to direct measurement light through the digit; a light-transmission measurement unit configured to measure a transmission index representing the proportion of the measurement light transmitted through the digit; and a digit characteristic parameter unit configured to receive one or more digit characteristic parameters indicative of: a skin tone of the digit; a nail texture of the digit; a nail thickness of the digit; a nail length of the digit; and a nail polish status of the digit; and wherein the device is configured to determine a blood glucose level measurement based on the transmission index, the depth of the digit and at least one of the digit characteristic parameters.

[0012] By using a depth of the digit of the subject in combination with one or more additional digit characteristic parameters to determine a blood glucose measurement, non-invasive measurements of blood glucose can be made more accurate than has previously been possible.

[0013] In the following, the blood glucose level sensing device may be referred to as the ‘sensing device’, or simply as the ‘device’.

[0014] Non-invasive measurements are understood to mean measurements that are made without damaging the (digit of the) subject or drawing blood from the subject.

[0015] Preferably, the ‘digit’ of a subject refers to a finger of the subject. The present invention is not limited in this way, however. For example, the digit of the subject may also refer to a thumb of the subject.

[0016] The ‘depth’ of the digit refers to the distance between a top side of the digit (e.g., a side of a digit on which a nail is located) and a bottom side of the digit (i.e., a side of a digit on which the pad of the digit is located, the pad being a part of the digit opposite the nail of the digit). Suitably, the digit depth is measured along an axis that is substantially perpendicular to the plane of the top and bottom sides of the digit. The depth of the digit may refer to the depth of a particular point through the digit. Alternatively, the depth of the digit may refer to an average depth of the digit, or more suitably a particular portion of the digit. For example, the depth of the digit may be the average depth of a portion of the digit at the distal end of the digit (e.g., a distal end portion of the digit). Said distal end portion of the digit may be defined as the portion of the finger covered by the nail. Suitably, the measurement light generation element is configured to direct light through an end portion of a digit, such as a portion having a nail. In these examples, the light is directed through the nail of a digit. Suitably, the light may be directed through the nail first, and then through the remainder of the digit afterward. Alternatively, the light may be directed through the remainder of the digit first, such that the light exits the digit through the nail. However, the present invention is not limited to the examples above, and the light may instead be directed to travel through alternative portions of the digit, such as portions of the digit in which there is not a nail.

[0017] The light-transmission measurement unit may be positioned opposite the measurement light generation element, such that, during measurement of a digit, the light-transmission measurement unit is arranged on a first side of the digit, and the measurement light generation element is arranged on a second side of the digit opposite the first side of the digit. For example, the light-transmission measurement unit may be arranged so as to be adjacent a pad of a digit, whilst the measurement light generation element is arranged to be adjacent a fingernail of a digit. Suitably, in such examples, the light transmission measurement unit and measurement light generation element may be arranged on opposite sides of a cavity into which a subject digit may be placed.

[0018] The sensing device may use values for each of the digit characteristic parameters, a value for only a single digit characteristic parameter, or a specific subset of digit characteristic parameters as part of the calculation to determine the blood glucose level.

[0019] The skin tone parameter quantises the colour of a subject’s skin, which affects the way that light from the measurement light generation element is absorbed and / or reflected. The skin tone parameter may refer to the skin tone of the digit generally, or may specifically refer to the skin tone of a particular portion of the digit. For example, the skin tone parameter may refer specifically to the skin tone of the pad of the digit.

[0020] The nail texture parameter quantises the relative ‘roughness’ of the nail (which affects the reflection of light from the nail) and / or the relative transparency of the nail (which affects the amount of light which passes through the nail). The nail ‘roughness’ may suitably be characterised in how many ridges the nail has.

[0021] The nail thickness parameter indicates the thickness of the nail. This may refer to the average thickness of the nail, or to the thickness of a specific point on the nail.

[0022] The nail length parameter relates to the length of the nail, which affects the amount of a digit that may be inserted between the measurement light generation element and the light-transmission measurement unit. For instance, in examples of the device whether the subject is required to insert their finger into a cavity (e.g., between the measurement light generation element and the light transmission measurement unit), a distal tip of the nail may contact a far end of the cavity, such that the finger is prevented from moving any further into said cavity. This will impact the portion of the finger which light from the light measurement generation unit is directed through, which may further impact the measured transmission index and measured blood glucose level. The nail length parameter may indicate the length of the nail measured from the point that (e.g., a central portion of) the nail emerges from under the skin of the digit to the distal tip of (e.g., the central portion of) the nail. Alternatively, the nail length parameter may indicate the length of the overhang of the nail from the distal tip of the digit. E.g., how far past the distal tip of the digit the nail extends.

[0023] The nail length parameter is measured along a direction that is parallel to the longitudinal direction in which the digit extends. E.g., the nail length parameter is measured along a direction that is parallel to the direction of growth of the nail.

[0024] The measured length of the nail may be the maximum value that the nail achieves. For example, when the nail length parameter relates to the amount of overhang of the nail, there might be varying degrees of overhang along a width of the nail. In this case, the nail length parameter may be taken as the biggest overhang value.

[0025] The nail polish status parameter accounts for the effect that varying nail polishes can have on light from the measurement light generation element. The nail polish status parameter may quantise at least one or more of: the reflectivity (e.g., glossiness) of the nail polish, the colour of the nail polish, the texture of the nail polish, the opacity of the nail polish, and the thickness of the nail polish, all of which will affect the amount of light from the measurement light generation element that reaches the light-transmission measurement unit. Alternatively, the nail polish parameter may simply indicate whether or not the user is wearing nail polish.

[0026] The nail polish status parameter may also account for nail paints.

[0027] The inclusion of one or more of these parameters into the calculation of the blood glucose measurement advantageously allows various effects on the light directed through the digit to be accounted for and mitigated, such that a more accurate final blood glucose measurement is made.

[0028] In some embodiments, the device is configured to determine a blood glucose level measurement based on the transmission index, the depth of the digit, and at least two, or at least three, or at least four, of the digit characteristic parameters.

[0029] In some examples, the measurement light generation element is configured to generate infrared light.

[0030] In some examples, the measurement light generation element is configured to generate visible light. More suitably, the measurement light generation element is configured to generate light having a wavelength greater than or equal to 640 nm and less than or equal to 660 nm.

[0031] In some examples, the measurement light generation element is a laser transmitter. This advantageously allows a narrower range of wavelengths to be transmitted between the measurement light generation element and the light-transmission measurement unit, making it easier to model the relationship between the drop in transmission index and the percentage of light absorbed by the blood glucose.

[0032] Suitably, the laser transmitter may be a 100 mW laser module.

[0033] Optionally, the laser transmitter outputs light within the red spectral region. Preferably, the output spectral width of the laser transmitter is between 560 nm and 699 nm. In some examples, the light-transmission measurement unit may comprise a photosensitive sensor module. In such a case, the output from the photosensitive sensor module, typically a voltage, may be used as the transmission index.

[0034] Suitably, the device may further comprise a filtering buffer circuit connected to the photosensitive sensor module.

[0035] The device may further comprise a power supply for the sensing device. Said power supply may include one or more (e.g., rechargeable) batteries. Alternatively, the device may be connectable to a mains power supply.

[0036] In some examples, the device is configured to calculate the blood glucose level measurement using an equation derived by a supervised machine learning model.

[0037] In some examples, the blood glucose level measurement is calculated using an equation in the form of: blood glucose measurement = A*(transmission index) + B*( depth of the digit) + C*(digital characteristic parameter) + ..., where A, B and C are coefficients (e.g., determined using linear regression), and ... denotes the possibility of further digital characteristic parameters multiplied by further coefficients. For example, where the device is using three different digital characteristic parameters, the formula would be blood glucose measurement = A*(transmission index) + B*( depth of the digit) + C*(digital characteristic parameter 1) + D*(digital characteristic parameter 2) + E*(digital characteristic parameter 3).

[0038] In some examples, the supervised machine learning model is trained on a dataset containing a plurality of historic blood glucose level measurements measured invasively and respective digit depths, digit characteristic parameters and transmission indices.

[0039] In some examples, the digit characteristic parameter unit comprises an input module, the input module being configured to receive input of a digit characteristic parameter from an operator of the blood glucose level sensing device.

[0040] The input module may be a user interface into which the operator can input one or more digit characteristic parameters. Said user interface may be a touch screen, a series of buttons, or an audio receiver.

[0041] Alternatively, the input module may be a configured to receive the digit characteristic parameters from an external device, such as a laptop or a mobile device. The external device may suitably comprise a digital application into which the digit characteristic parameters may be entered, and a transmitter configured to transmit the digit characteristic parameters to a receiver of the input module.

[0042] In some examples, the device further comprises a temperature sensor configured to measure a temperature of the digit; and wherein the blood glucose level sensing device is configured to determine a blood glucose level measurement further based on the digit temperature.

[0043] The temperature sensor may be configured to contact the subject during measurement. Alternatively, the temperature sensor may be configured for non-contact measurements of the subject.

[0044] The temperature sensor may use light to determine the temperature of the digit.

[0045] The temperature sensor may be an MLX90614, Infra-Red thermometer. In some examples, the device further comprises a vibration sensor configured to measure an acceleration of the sensing device during transmission measurement; and wherein the light-transmission measurement unit is configured to adjust a voltage based on said acceleration.

[0046] Suitably, the vibration sensor is configured to measure vibrations at frequencies of between 5 and 25 Hz. Even more suitably, the vibration sensor is configured to measure vibrations at frequencies of between 10 and 15 Hz.

[0047] Strong scientific evidence indicates that the digits of a subject suffering from diabetes begin to vibrate at frequencies of 10-15 Hz during serious events such as a hypoglycemic episode. As such, the vibration sensor can be used to advantageously improve the accuracy of blood glucose measurements on the device, particularly in extreme cases.

[0048] Suitably, the vibration sensor may be a ADXL335, 3-axis accelerometer module.

[0049] In some examples, the device may comprise a fingerprint sensor.

[0050] The fingerprint sensor may be used to identify one of a plurality of subjects. Alternatively, the fingerprint sensor may be used to prevent unauthorised use of the device.

[0051] Suitably, the fingerprint sensor is a AS608 fingerprint reader sensor.

[0052] The digit-depth unit may measure the depth of the digit of the subject in any number of different ways.

[0053] For example, the digit-depth measurement unit may comprise: a displaceable member configured to be displaced in a first direction by the digit; and a time-of-flight sensor module configured to measure the displacement of the displaceable member in the first direction.

[0054] Alternatively, or additionally, the digit-depth unit may receive one or more values corresponding to the digit of a subject in the first direction. Said values may be inputted directly into the blood glucose level sensing device, and by extension the digit-depth unit, by the subject, or the values may be transmitted to the digit-depth unit electronically from a separate device, such as a mobile phone.

[0055] The first direction may be parallel to the direction of travel of light between the measurement light generation element and the light-transmission measurement unit. This advantageously means that the digit depth measurement value corresponds exactly to the amount of digit matter through which the light travels.

[0056] The digit-depth unit may be configured to store one or more values of digit depth. These values may correspond to one or more of: the depth of the digit of a subject at different points or portions on a single digit, the depth of points or portions of multiple different digits on a subject, the depth of points or portions of digits of multiple different subjects.

[0057] In some examples, the device further comprises a communications unit configured to connect to a network for transmission of the blood glucose value.

[0058] In some examples, the sensing device is further configured to sense or receive a device variance value which accounts for the variations in power of different measurement light generation elements and / or sensitivities / calibrations of the light-transmission measurement unit, wherein said device variance value is used to adjust the blood glucose level measurement. The device may comprise a device variance unit for sensing and / or receiving the device variance value(s).

[0059] In some examples, the device further comprises a calibration unit, wherein the calibration unit is configured to: receive an initial blood glucose level measurement of the subject performed by the sensing device; receive a reference blood glucose level measurement of the subject; and determine a calibration factor for the subject by comparing the initial blood glucose level measurement to the reference blood glucose measurement; wherein the sensing device is configured to determine one or more future blood glucose level measurements further based on the calibration factor.

[0060] The calibration unit calculates the calibration factor by comparing the reference blood glucose level measurement to a blood glucose measurement determined by the sensing device without calibration to determine a calibration offset, wherein this calibration offset is taken as the calibration factor.

[0061] Suitably, the reference blood glucose level measurement is a high-accuracy blood glucose measurement obtained from a high accuracy blood glucose measurement technique. For example, the high accuracy blood glucose level measurement may be obtained using a finger prick test, in which a drop of blood is extracted from a subject, and analysed using known techniques.

[0062] The device may be configured to perform multiple calibration offsets of a single user to obtain an average calibration offset, wherein the average calibration offset is taken as the calibration factor.

[0063] The calibration unit may be configured to store different calibration coefficients for different subjects.

[0064] The sensing device may be configured to identify different subjects using the sensing device, and apply the correct calibration factor to blood glucose level measurements of that subject. For example, the subject may be identified by taking their fingerprint on a fingerprint scanner. Alternatively, the subject may input a specific code into an input module.

[0065] In a second aspect of the invention, there is provided a blood glucose monitoring system comprising: a blood glucose level sensing device according to the first aspect; and an analysis device; and wherein: the blood glucose level sensing device is connectable to the analysis device to provide the analysis device with a plurality of historical blood glucose values pertaining to a subject; and the analysis device is configured to determine a risk factor representing the risk of the subject developing diabetes based on the plurality of blood glucose values.

[0066] In a third aspect of the invention, there is provided a method of non-invasively determining a blood glucose level of a subject via a digit of the subject, the method comprising the steps of: measuring or receiving a depth of the digit in the first direction; directing a measurement light through the digit in the first direction; measuring a transmission index representing the proportion of the measurement light transmitted through the digit; determining one or more digit characteristic parameters, each digit parameter indicative of: a skin tone of the digit; a nail texture of the digit; a nail thickness of the digit; a nail length of the digit; or a nail polish status of the digit; and determining a blood glucose level measurement based on the depth of the digit, the transmission index and at least one of the digit characteristic parameters. The invention includes any combination of any aspect with another aspect and / or any combination of any aspect with any optional feature described except where such a combination is clearly impermissible or expressly avoided.

[0067] Summary of the Figures

[0068] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0069] Fig. 1 shows a block diagram of a sensing device according to a first example of the invention.

[0070] Fig. 2 shows a perspective view of a sensing device according to a second example of the invention.

[0071] Fig. 3 shows a cross-sectional perspective view of the sensing device of Fig. 2

[0072] Fig. 4 shows an example method of performing a non-invasive blood glucose level measurement.

[0073] Figs. 5A-D show screenshots of the user interface of a mobile phone application and associated steps that may be used to input digit characteristic parameters into the sensing devices of Figs. 1 -3.

[0074] Fig. 6 shows a graphical plot of blood glucose measurements made using both a transmission index and digit-depth measurements.

[0075] Figs. 7A-B show graphical comparisons of blood glucose measurement results obtained from sensing devices, comparing the effect of not using a skin tone parameter with using a skin tone parameter.

[0076] Detailed Description of the Invention

[0077] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0078] Fig. 1 shows a block diagram of a sensing device 100 according to a first example of the invention. The sensing device 100 is configured to perform a non-invasive blood glucose level measurement of a subject.

[0079] The sensing device 100 comprises a digit-depth unit 120, a measurement light generation element 140, a light-transmission measurement unit 160, a digit characteristic parameter unit 180 and a controller 190.

[0080] The digit-depth unit 120 is configured to receive and / or measure the depth of a digit of the subject. When the digit-depth unit 120 is configured to receive signals, the digit-depth unit 120 may include a receiver (not shown) for receiving digit-depth values from an external device. The digit-depth unit 120 may further comprise a transmitter (not shown) for transmitting digit-depth values measured or stored on the sensing device 100. A specific, but non-limiting, example of how the depth of the digit of the subject is measured is described in detail in relation to Figs. 2 and 3 below. The measurement light generation element 140 is configured to generate and transmit a beam of light through the digit of the subject, and the light transmission measurement unit 160 is configured to measure the beam of light after it has passed through the subject digit. Along its path between the measurement light generation element 140 and the light transmission measurement unit 160, a percentage of the beam of light will be absorbed. More particularly, as the beam of light travels through the digit, light from the beam will be absorbed by the blood in the digit of the subject. By comparing the emitted beam of light to the measured beam of light, a transmission index of the beam of light can be determined by the sensing device 100, or more specifically the light-transmission measurement unit 160.

[0081] In this example, the measurement light generation element 140 and light-transmission measurement unit 160 are arranged on opposite sides of a cavity 106 in the sensing device 100, into which the digit of the subject is insertable. In this way, the subject digit is placeable into the cavity 106 between the measurement light generation element 140 and the light-transmission measurement unit 160, such that a beam of light generated by the measurement light generation unit 140 and directed toward the lighttransmission measurement unit 160 passes through the digit along its trajectory (see Fig. 2 for a more specific example of this). Preferably, the measurement light generation element 140 and the lighttransmission measurement unit 160 are arranged around a portion of the cavity 106 in which a distal portion of the digit of the subject (i.e. , a portion of the digit having a nail) naturally comes to rest. This may be in an end portion of the cavity 106. Measuring the distal portion of the subject’s digit advantageously reduces the necessary size of the cavity, and thus the necessary size of the device. However, the sensing device 100 is not limited in the above way, and the skilled person having read this disclosure would recognise alternative ways in which the measurement light generation element 140 and light transmission measurement unit 160 may be arranged so that a digit of the subject is placed in the beam of light path between the two.

[0082] The digit characteristic parameter unit 180 is configured to receive one or more digit characteristic parameters indicative of one or more of a skin tone of the digit; a nail texture of the digit; a nail thickness of the digit; a nail length of the digit; and a nail polish status of the digit. These digit characteristic parameters represent numerical quantifications of the various characteristics of the digit. For example, a digit characteristic parameter for nail polish may be T for the presence of nail polish, and ‘0’ for the absence of nail polish. Additionally or alternatively, a digit characteristic parameter for nail texture may be ‘0’ for a clear nail, T for a normal nail, and ‘2’ for a hard nail. The digit characteristic parameters, and their quantification, is discussed in more detail in relation to Figs. 5A-D below.

[0083] In this example, the digit characteristic parameter unit 180 includes an input module 182, via which the subject can input digit characteristic parameters into the digit characteristic parameter unit 180. This input module may be a touch screen, a series of buttons, or a microphone. Alternatively, digit characteristic parameters may be transmitted to the input module 182 of the digit characteristic parameter unit 180 digitally. For example, a subject may input one or more digit characteristic parameters into an application on a mobile phone (e.g., see Figs. 5A-D), and then these digit characteristic parameters can be transmitted to the input module 182. It is noted that the present disclosure is not limited to an input module 182 that is specifically a part of the digit characteristic unit 180, however. Instead, the input module may be a part of the sensing device 100 more generally, and be usable to receive other parameters such as digit depth values, and reference blood glucose level measurements (for use in relation to the calibration unit 198 discussed below.

[0084] The controller 190 is connected to each of the components of the sensing device 100 (e.g., including the digit-depth unit 120, the measurement light generation element 140, the light-transmission measurement unit 160 and the digit characteristic parameter, as well as the further components of the sensing device 100 which are discussed below), and is configured to coordinate the blood glucose level measurements. The controller includes a CPU 191 for controlling the other components of the device, as well as a memory 192 which is usable to store values such as subject digit depths, subject digit characteristic parameters, transmission indexes, blood glucose level measurements etc.

[0085] In use, the controller 190 of the sensing device 100 is configured to use the digit-depth value(s) from the digit-depth unit 120, the transmission index determined from the beam of light generated by the measurement light generation element 140 and measured and light-transmission measurement unit 160, and the one or more digit characteristic parameters from the digit characteristic parameter unit 180 to determine a blood glucose level measurement.

[0086] As mentioned previously, a portion of the beam of light generated by the measurement light generation element 140 will be absorbed as it passes through the digit of the subject, such that the light intensity measured by the light-transmission generation unit 160 will be smaller than the outputted light intensity of the measurement light generation element 140. Either the controller 190 or the light-transmission measurement unit 160 is configured to use this difference to calculate a transmission index of the beam of light for the subject digit.

[0087] The transmission index of light through the digit of the subject has previously been found to directly correlate to the subject’s blood glucose level, and so the transmission index can be used to make an estimate of the blood glucose level.

[0088] However, the transmission index is also affected by additional factors. For example, a larger digit-depth will mean a larger amount of material through which the beam of light has to travel, causing additional absorbance and thus affecting the transmission index. Additionally, digit characteristics such as digit skin tone, digit nail texture, digit nail thickness, and digit nail polish status will all affect the percentage of light able to travel between the measurement light generation element 140 and the light-transmission measurement unit 160, whilst digit nail length can affect how it is possible to position the digit between the measurement light generation unit 140 and the light transmission measurement unit 160. All of these digit characteristics will thus affect the transmission index, and the accuracy of the blood glucose level measurement made based on the transmission index alone.

[0089] The sensing device 100 of the present embodiment accounts for these problems by factoring at least the digit-depth and at least one additional digit characteristic into the blood glucose measurement, thereby improving the accuracy of the result. In some, non-limiting, examples, the sensing device 100 uses an equation in the following form to determine blood glucose level: Blood Glucose Level = A*(transmission index) + B*(finger depth) + C*(digit characteristic parameters 1) + where A, B and C are coefficients (e.g., calculated using linear regression), and ... denotes the possibility of further digit characteristic parameters multiplied by further coefficients (e.g., D, E, F etc.). The ... may also denote the inclusion of other relevant parameters, which are discussed in the following disclosure. This advantageously provides a simple equation that can be used to produce highly accurate results.

[0090] The coefficients can be calculated using a supervised machine learning model, which may be trained based on a dataset containing a plurality of historic glucose level measurements measured invasively and respective digit depths, digit characteristic parameters and transmission indices. However, the invention is not limited in this way, and the skilled person having read the present disclosure will recognise alternative equation forms, and alternative ways of deriving said equation, that may be used.

[0091] The sensing device 100 further comprises a temperature sensor 194 and a vibration sensor 196, both of which are connected to the controller 190 and are usable to further improve the blood glucose level measurement results. In particular, the temperature sensor 194 is configured to measure the temperature of the digit of the subject when the digit is inserted into the cavity 106. This may be achieved through direct contact with the digit, or the temperature sensor 194 may be a non-contact temperature sensor (e.g., an infrared temperature sensor). The controller 190 can then choose to use to incorporate the temperature value into the blood glucose level measurement equation discussed above, wherein the temperature value may be multiplied by a temperature coefficient determined in a similar manner to the other coefficients discussed above.

[0092] Similarly, the vibration sensor 196 is configured to measure vibrations of a digit inserted into the cavity 106, which the controller 190 can also decide to incorporate into the blood glucose level measurement equation discussed above.

[0093] The sensing device also includes a calibration unit 198, which is usable by the controller 190 to provide a further calibration factor to the blood glucose level measurement equation discussed above.

[0094] In use, the calibration unit 198 is configured to receive a first blood glucose level measurement from the controller 190 that has been made without input from the calibration unit 198 (e.g., no calibration factor is used in the calculation of the blood glucose level measurement). The calibration unit is also configured to receive a reference blood glucose level measurement. Said reference blood glucose level measurement may be inputted into the sensing device 100 directly by the user, for example using the input module 182. The reference blood glucose level measurement is intended to be a highly accurate representation of the subject’s blood glucose level at the time that the first blood glucose level measurement is made, and so may have been made by an invasive technique such as a finger prick test.

[0095] The calibration unit 198 is configured to determine a calibration factor based on the difference between the first blood glucose measurement and the reference blood glucose measurement. For example, the calibration factor may be exactly the difference between the first blood glucose level measurement and the reference blood glucose level measurement, thought he calibration unit 198 is not limited to this approach. The calibration unit 198 then provides the determined calibration to the controller 190, which can incorporate the calibration factor into future non-invasive blood glucose level measurements.

[0096] The sensing device 100 further comprises a fingerprint sensor 199, which is usable by the subject to identify themselves to the device 100. For example, the controller 190 may store a number of fingerprint patterns relating to different subjects who have used the device 100 (these may, for example, be stored in the memory 192 of the controller 190). The controller 190 may then compare the fingerprint of a subject currently using the fingerprint sensor 199 to the saved fingerprint patterns to determine the subject currently using the device 100. Advantageously, this may allow the sensing device to use additional information about that subject (i.e., digit depth, calibration factor etc.) which is saved in the memory 192 of the controller 190, saving on the amount of measurements / set up required for future blood glucose level measurements.

[0097] In some examples, the sensing device may also include one or more of a display for displaying information (e.g., blood glucose measurements), and a transmitter / receiver for communication with external devices (e.g., to receive digit depths and characteristic parameter values of subjects, and / or to transmit measured blood glucose values).

[0098] Figs. 2 and 3 show a sensing device 200 according to a second example of the invention. More specifically, Fig. 2 shows a perspective view of the sensing device 200, and Fig. 3 shows a cross- sectional perspective view of the sensing device 200. The sensing device 200 is similar to the sensing device 100 of Fig. 1 , and like features are given like reference numerals incremented by 100.

[0099] The sensing device 200 comprises a housing 202 which encloses an internal space 204. An external surface of the housing includes a display 212 (e.g., for showing blood glucose measurement results and / or for inputting characteristic parameters of the digit), as well as a first button 214 for initiating a blood glucose measurement and a second button 216 for turning the sensing device 200 on and off.

[0100] The external surface of the housing 202 further includes a recessed portion 206 which is shaped to receive a digit of a subject (not shown). More particularly, the recessed portion 206 is positioned at an edge of the housing 202 between a first housing side 202a and a second housing side 202b that is angled relative to the first housing side 202a. In this way, the recessed portion 206 includes a first exposed side on the first housing side 202a, and a second exposed side on the second housing side 202b.

[0101] A lid 210 is attached to the housing 202, said lid 210 being movable relative to the housing 202 between a closed state in which the lid 210 partially covers the recessed portion 206 (e.g., the lid 210 covers the first exposed side of the recessed portion 206 in the first housing side 206a, but not the second exposed side of the recessed portion 206 in the second housing aide 206b) and an open state in which the recessed portion 204 is uncovered. In use, the subject’s digit is placed into the recessed portion 206 when the lid 210 is in the open state. The lid 210 is then moved to the closed state so that the digit is partially enclosed within the recessed portion 206 between the housing 202 and the lid 210, and blood glucose measurements are performed as described below. In the present example, the lid 210 is hingedly attached to the housing 202, such that the lid 210 ‘swings’ relative to the housing 202 between the open and closed states. Further, the housing 202 includes a groove 205 around the recessed portion 204 that forms a matching fit with the lid 210, such that the lid 210 is received in the groove 205 in the closed state to form a flush surface with the first housing side 202a. However, the present invention is not limited to sensing devices which include these features.

[0102] The sensing device 200 also comprises a digit-depth unit 220 for measuring the depth of a subject’s digit, which includes a digit contact element (e.g., a displaceable member) 222 having a digit contact surface 223, a finger element 224 attached to and protruding from the digit contact element 222, and a finger element sensor 226.

[0103] As shown in Fig. 2, the digit contact element 222 is positioned within the recessed portion 206 with the digit contact surface 223 facing toward the position of the lid 210 in the closed state. In use, the digital contact surface 223 is configured to contact the digit of the subject when said digit is inserted into the recessed portion 206.

[0104] The digit contact element 222 is movably coupled to the housing 202 along a vertical axis indicated by arrow 201 , such that at least the digit contact surface 223 is movable between a relaxed state and a displaced state. More particularly, the housing 202 includes a pair of rods 207 which protrude into the recessed portion 206 along the vertical axis 201 from a bottom surface of the recessed portion 206 (e.g., a surface of the recess portion 206 opposite the first exposed side of the recessed portion 206 in the first housing side 202a). These rods 227 slidably engage a pair of holes 227 that extend into the digit contact element 222, such that the digit contact element 222 is movable onto and off of the rods 207 in the vertical direction 201 . In the present example, the holes 227 extend all the way through the digit contact element 222 from a surface of the digit contact element 222 opposite the digit contact surface 223 to the digit contact surface 223. The present disclosure is not limited in this way however, and the holes 227 may extend from the surface of the digit contact element 222 opposite the digit contact surface 223 to a point within the digit contact element 222.

[0105] In the relaxed state, the digit contact surface 223 is proximal to the position of the closed state lid 210. For example, the distance between the digit contact surface 223 and the closed state lid 210 is no more than 10 mm, 9 mm, 8 mm, 7 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2 mm, or 1 mm. In some examples, the digit contact surface 223 in the relaxed state may contact the closed state lid 210.

[0106] In the displaced state, the digit contact surface 223 is further from the position of the closed state lid 210 than when the digit contact element 222 is in the relaxed state. More particularly, the distance between the digit contact surface 223 and the closed state lid 210 when the digit contact element 222 is in the displaced state is greater than the distance between the digit contact surface 223 and the closed state lid 210 when the digit contact element 222 is in the relaxed state. In some examples, the distance between the digit contact surface 223 and the closed state lid 210 when the digit contact element 222 is in the displaced state may be: 25 mm, 24 mm, 23 mm, 22 mm, 21 mm, 20 mm, 19 mm, 18 mm, 17 mm, 16 mm, 15 mm, 14 mm, 13 mm, 12 mm, 11 mm, 10 mm, 9 mm, or 8 mm. The displaced state and the relaxed state may be defined by a difference in distance of the digit contact surface 223 from the closed state lid 210 in the two states. For example, the distance between the digit contact surface 223 and the closed state lid 210 in the displaced state may be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm or 20 mm greater than the distance between the digital contact surface and the closed state lid in the relaxed state.

[0107] At rest (e.g., in the absence of external forces), the digit contact element 222 remains in the relaxed state. In some examples, the digit contact element 222 is resiliently biased (e.g., by springs, not shown) to the relaxed state.

[0108] The digit contact element 222 is movable to the displaced state by the application of a force to the digit contact element 222. More particularly, said force is applied to the digit contact surface 223 by a digit of the subject inserted into the recessed portion 206.

[0109] In the present example, the digit contact element 222 is a compressible body, such that the digit contact surface 223 is pressable toward a bottom surface of the digit contact element 222 (e.g., the surface of the digit contact element 222 that is opposite the digit contact surface 223). More particularly, the digit contact element 222 is uncompressed in the relaxed state, and is movable to the displaced state via the application of force to the digit contact surface 223. Further in this example, the bottom surface of the digit contact element 222 is in contact with the bottom surface of the recess portion 206, so as to be held in place vertically whilst the digit contact surface 223 is compressed toward it. The digit contact surface 223 in this example is rigid, such that the digit contact surface 223 maintains the same shape as the digit contact element 222 is compressed. Advantageously, this allows the finger element 224, which is attached to the digit contact surface 223, to be vertically displaced by an amount exactly equal to the maximum vertical displacement caused by the digit, such that the digit depth measurement (made based on the sensed displacement of the finger element 224 as described below) can be made more accurate. However, the present disclosure is not limited in this way, and the digit contact surface 223 may instead be flexible. For example, the digit contact surface 223 may at least partially conform to the shape of the digit as it is displaced downward.

[0110] In further alternative embodiments, the digit contact element 222 may instead be incompressible. In this case, movement of the digit contact element 222 between the relaxed and displaced states may correspond to movement of the entire digit contact element 222 along the vertical axis 201 . For example, in the relaxed state, the bottom surface of the digit contact element 222 (the surface of the digit contact element 222 opposite the digit contact surface 223) may be displaced away from a bottom surface of the recessed portion 206 (the surface of the recessed portion 206 opposite the first exposed side of the recessed portion 206), and in the displaced state, the bottom surface of the digit contact element 222 may contact the bottom surface of the recessed portion 206.

[0111] The finger element 224 of the digit-depth unit 220 protrudes from the digit contact element 222 and into the internal space 204 of the housing 202 via a slot 208 through a wall of the recessed portion 206. In the present example, the finger element 224 is configured to move with the digit contact surface 223, so that a downward movement of the digit contact surface 223 causes a corresponding downward movement of the finger element 224.

[0112] Movement of the finger element 224 is detected by the finger element sensor 226, which is positioned within the internal space 204 of the housing 202. More particularly, the finger element sensor 226 is configured to detect the position of the finger element 224 relative to the finger element sensor 226. As the finger element 224 moves with the digit contact element 222, the position of the finger element 224 changes relative to the finger element sensor 226, which is detected by the sensor 226.

[0113] In the present example, the finger element sensor 226 is vertically aligned with the finger element 224, but in alternative examples the finger element sensor 226 may be placed in any position within the internal space 204 from which it can detect the movement of the finger element 224.

[0114] To perform the digit-depth measurement, the subject places their digit onto the digit contact surface 223 of the digit contact element 222 whilst the lid 210 is in the open state. When the spacing between the digit contact surface 223 and the closed state lid 210 is smaller than the depth of the digit, the closure of the lid 210 then forces the digit, and the digit contact element 222, toward the bottom surface of the recessed portion 206. This causes a corresponding movement in the finger element 224, which is detected by the finger element sensor 226. The finger element sensor 226 then uses this information to determine the depth of the digit.

[0115] The sensing device 200 further comprises a measurement light generation element 240 and a lighttransmission measurement unit 260, which work in conjunction to determine a transmission index of a digit placed into the recessed portion 206. The measurement light generation element 240 and the lighttransmission measurement unit 260 are arranged on opposite sides of the recessed portion 206, and thus are on opposite sides of a digit placed within the recessed portion 206. In this way, light generated by the measurement light generation element 240 passes through the digit placed in the recessed portion 206 prior to reaching the light-transmission measurement unit 260.

[0116] More particularly, the measurement light generation element 240 comprises a laser that is arranged within the housing internal space 204, and is configured to transmit light through the recessed portion 206 and toward the light-transmission measurement unit 260 contained in the lid 210. In this example, the measurement light generation element 240 is aligned with holes 225 in the bottom surface of the recessed portion 206 and the digit contact element 222 respectively, such that the light from the measurement light generation element 240 has an uninterrupted path into the recessed portion 206. This advantageously reduces the amount of light absorption taking place outside of the subject’s digit, resulting in a transmission index that is better correlated to the light absorption in the digit. However, the present invention is not limited in this way. For example, in some alternatives the digit contact element 222 and / or bottom surface of the recessed portion 206 may not have holes 225 (e.g., may be solid), and the additional absorption may instead be accounted for by additional terms in the blood glucose measurement equation. The sensing device 200 further comprises a digit characteristic parameter unit (not shown), which is similar to the digit characteristic parameter unit 180 shown in Fig. 1 . More particularly, the digit characteristic parameter unit is configured to receive digit characteristic parameters corresponding to one or more of a skin tone, nail texture, nail thickness, nail length, nail paint status, and nail polish status. These may be received via digital transmission from an external device, or may be inputted into a user interface (e.g., the display 212 may also be a touch screen into which digit characteristic parameters can be inputted).

[0117] The digit characteristic parameter may be incorporated into the circuit board 280 of the sensing device 200, which is also configured to control the measurement light generating element 240. The circuit board may further comprise a controller (not shown) for controlling the sensing device 200 in a similar way to the sensing device 100. Alternatively, the circuit board 280 may include a receiver for receiving instructions from an external device (e.g., a mobile phone, laptop, or dedicating sensing device controller device), and the sensing device 200 may instead be controlled by said external device.

[0118] The sensing device 200 uses the results / parameters obtained from the digit-depth unit 220, the measurement light generation element 240, the light-transmission measurement unit 260 and the digit characteristic parameter unit to arrive at a blood glucose measurement in a corresponding way to the sensing device 100.

[0119] Fig. 4, shows a method of performing a non-invasive blood glucose level measurement of a digit of a subject according to an example of the present invention, which includes steps 302-310. This method may be performed by the sensing devices 100200 of Figs. 1-3, but is not limited to being performed on these devices.

[0120] In step 302, the digit-depth of a subject digit along a first direction is measured or received. The depth of the digit will preferably be measured at a point on the digit where the line along which the depth is measured (i.e., the first direction) includes a portion of a nail, though the present method is not limited in this way. The digit-depth may be measured using one of the sensing devices of Figs. 1-3, or by a separate and known measurement apparatus. Alternatively, the depth may already be known (e.g., because it has already previously been measured), and stored, for example, on a memory. In which case, the depth may be retrieved from said memory.

[0121] In step 304, measurement light is directed through the digit along the first direction. Preferably, the measurement light is directed through the same portion of the digit whose depth was measured in step 302. The measurement light may be from one of the measurement light generation units included in the sensing devices 100, 200, or may be some other source of light.

[0122] In step 306, a transmission index is determined based on the proportion of measurement light transmitted through the digit. More particularly, the measurement light will be absorbed as it passes through the digit. By comparing the amount of measurement light that is detected after passing through the digit compared to the amount of measurement light that was generated and directed at the digit, the amount of absorbance in the digit, and thus a transmission index can be determined. In step 308, one or more digit characteristic parameters are determined. These correspond to one or more characteristics of the digit, including a digit: skin tone, nail texture, nail thickness, nail length and nail polish status. The digit characteristic parameters may be measured. However, the present disclosure is not limited in this way. For example, the digit characteristics may have been measured in the past, and in the present are retrieved from a storage.

[0123] In step 310, a blood glucose level measurement is determined based on the depth of the digit, the transmission index and at least one of the digit characteristic parameters. The blood glucose level measurement may further be based on additional factors, such as a digit temperature, the amount the digit was vibrating at the time the measurement light was directed through the digit, and a calibration factor (determined as discussed in relation to Fig. 1).

[0124] Figs. 5A-5D show a mobile application 400 having a calibration input portion 402, a skin tone parameter selection portion 410, a nail characteristic portion 430 and a measurement activation slider 450. The mobile application 400 may be used to: control the sensing devices 100 200 of Figs. 1 -3, provide digit characteristic parameters to the sensing devices of Figs. 1 -3, and / or receive blood glucose level measurements from the sensing devices 100 200 of Figs. 1 -3.

[0125] Fig. 5A shows the calibration input portion 402, which may be used to control a calibration unit (either on the sensing device or forming part of the mobile application 400 software). The calibration input portion 402 includes a reference blood glucose level measurement input portion 404 and a sensing device (e.g., one of the sensing devices 100 200) blood glucose level measurement input portion 406. In use, the sensing device blood glucose measurement input portion 406 of the mobile application 400 receives a blood glucose level measurement from a sensing device, wherein the measurement is made without a calibration factor. This blood glucose level may be transmitted to the mobile application 400 digitally, or it may be inputted directly into the sensing device blood glucose level measurement input portion 406 by a user of the mobile application 400. Correspondingly, the reference blood glucose level measurement input portion 404 receives a reference blood glucose level measurement that is determined using an accurate blood glucose level measurement technique, such as a finger prick test. The two values are then comparable either on the mobile application 400 or after being transmitted to a sensing device to determine a calibration factor, which may be used in future blood glucose level measurements.

[0126] Fig. 5B shows the selection of a skin tone parameter using the skin tone parameter selection portion 410. More specifically, the subject is able to select a skin tone parameter using a slidable button 412. As the slidable button 412 is moved from left to right on the page, the indicated skin tone becomes progressively darker, as shown diagrammatically by reference numerals 414-422. In this way, the subject is able to select a skin tone that at least largely reflects the skin tone of their own digit. This may then be transmitted electronically to the sensing device 100 200 for use as part of the calculation of the blood glucose level measurement.

[0127] Fig. 5C shows the selection of various nail characteristic parameters using the nail characteristic portion 430. More specifically, the nail characteristic portion 430 is usable to select nail texture and nail paint digit characteristic parameters 432 433. The nail texture digit characteristic parameter 432 may be selected from three options: ‘clear’, ‘normal’ and ‘hard’, as shown by reference numerals 434-438. These options may refer to the relative number of ridges on the nail. The nail paint digit characteristic parameter 433 may be selected from two options, which respectively indicate the presence or absence of nail paint. The selection of these options is shown by reference numerals 440-442. The selected combination of nail texture digit characteristic parameter 432 and nail paint digit characteristic parameter may be transmitted to the sensing device 100200 for use as part of the calculation of the blood glucose measurement.

[0128] Fig. 5D shows the measurement activation slider 450, which includes a slider button 452. Sliding the slider button 452 from left to right prompts the mobile application 400 to send a command to the sensing device to take a blood glucose level measurement. This action may further prompt the mobile application 400 to transmit the digit characteristic parameters selected by the subject on the mobile application 400 to the sensing device for use in the blood glucose level measurement.

[0129] Fig. 6 shows a graphical plot of blood glucose measurements made using a sensing device that incorporates both a transmission index and digit-depth measurement into the calculation. The measurements used by the sensing device are shown in Table 1 below. Table 1

[0130] In the above table, the voltage measurement quantifies the transmission index, the device variance accounts for differences in what specific sensing device is user to measure the blood glucose, and the BGL (Finger prick) column refers to blood glucose measurements made using a finger prick test, which are used as the reference values against which the non-invasive measurements are compared. Further in the above table, the BGL (sensing device) (mg / DL) column, which represents the blood glucose level measurements made using the sensing device, is calculated using

[0131] BGL (without skin tone parameter} = (12.25051 * Digit depth.} + (0.12645 * Voltage} — Device variance — 195.35175

[0132] The plot shown in Fig. 6 shows a comparison of the blood glucose level measurement results obtained from a non-invasive technique (i.e., a technique using the transmission index and digit-depth measurements) with an accurate reference value of what the blood glucose level measurement should be (i.e., the blood glucose level measurements made using the finger prick test) . The closer the results are to the dotted line, the more accurate the non-invasive measurement is.

[0133] The plot also includes a Clarke’s error gride overlaid on top, which is a well-known approach of analysing the accuracy of blood glucose measurements by grouping the obtained results into one of five zones A-E.

[0134] Zone A includes results which are within 20% of the reference result, zone B includes results which are more than 20% away from the reference result, but that would not lead to inappropriate treatment, zone C refers to results which would lead to unnecessary treatment, zone D refers to potentially dangerously inaccurate results (i.e., results that would potentially lead to the failure to detect hypoglycemia or hyperglycemia), and zone E refers to points that would confuse treatment for hypoglycemia with hyperglycemia and vice versa.

[0135] As shown in the Fig., the vast majority of the results fall within either zone A or zone B, with the majority of these results falling within zone A. Figs. 7A-B show graphical comparisons of blood glucose measurement results obtained from non- invasive sensing devices that respectively did and didn’t use a skin tone parameter.

[0136] More specifically, the non-invasive sensing devices were used to measure a transmission index (determined using a voltage measurement corresponding to an amount of light that passed through a digit) and a depth of a digit of each of 28 subjects, which were then used to calculate a blood glucose measurement. One of the two sensing devices, which may correspond to the one of the sensing devices 100 200, also included a digit characteristic parameter related to skin tone as part of its calculation, whilst the other of the two sensing devices did not. The same 28 subjects also had their blood glucose level measured using a finger prick test, which is a well-known and highly accurate invasive measurement technique in which a drop of blood is extracted from a finger and analysed in a machine. The results obtained are shown in Table 2 below.

[0137] Table 2

[0138] In the above table, the voltage measurement quantifies the transmission index, the device variance accounts for differences in what specific sensing device is used to measure the blood glucose, and the BGL (Finger prick) column refers to blood glucose measurements made using a finger prick test, which are used as the reference values against which the non-invasive measurements are compared. Further in the above table, the ‘BGL without skin tone (mg / dL)’ column, which represents the blood glucose level measurement made using the sensing device, is calculated using:

[0139] BGL (without skin tone parameter} =

[0140] 142.711924 — (1.278098 * Digit depth} — (0.004041 * Voltage} — Device variance whilst the ‘BGL with skin tone (mg / dL)’ is calculated using:

[0141] BGL (with skin tone parameter =

[0142] 81.8415 + (2.3749 * Digit depth} + (0.002183 * Voltage} — (1.6446 * Skin tone} — Device variance.

[0143] Figs. 7A-B show the percentage error of the non-invasive blood glucose measurements made with and without skin tone when compared to the invasive blood glucose measurements made using the finger prick test. Said percentage errors being calculated using the following equation:

[0144] More particularly, Fig. 7A shows a bar chart in which the percentage errors of the blood glucose level measurements performed on each subject are lined up side by side. Fig. 7B shows a scatter graph in which each point represents one of the subjects. The x coordinate of each of these subject points represents the percentage error of the measurement made on the subject that didn’t use skin tone, whilst the y coordinate of each subject point represents the percentage error of the measurement made on the subject that used the skin tone as part of the calculation. In this way, points falling below the diagonal line represent occasions where the blood glucose level measurement made of a subject that used the skin tone parameter as part of the calculation were more accurate than the blood glucose level measurement made on the same subject where a skin tone parameter was not used.

[0145] As shown, in all but seven of the 28 cases, the percentage error of the non-invasive measurement made using the skin tone parameter is lower than the percentage error of the non-invasive measurement made without the skin tone parameter. Additionally, the average percentage error of the measurements made with the skin tone parameter is only 6%, compared with an average percentage error of 12% for the measurements made without the skin parameter. It is thus clear that the inclusion of the skin tone parameter allows the accuracy of blood glucose measurements to be improved.

[0146] ***

[0147] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0148] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0149] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0150] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0151] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0152] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:

1. A blood glucose level sensing device for non-invasive blood glucose level measurement of a subject, the device comprising: a digit-depth unit configured to measure or receive a depth of a digit of the subject; a measurement light generation element configured to direct measurement light through the digit; a light-transmission measurement unit configured to measure a transmission index representing the proportion of the measurement light transmitted through the digit; and a digit characteristic parameter unit configured to receive one or more digit characteristic parameters indicative of: a skin tone of the digit; a nail texture of the digit; a nail thickness of the digit; a nail length of the digit; and a nail polish status of the digit; and wherein the device is configured to determine a blood glucose level measurement based on the transmission index, the depth of the digit and at least one of the digit characteristic parameters.

2. The device according to claim 1 , wherein the measurement light generation element is configured to generate light having a wavelength greater than or equal to 640 nm and less than or equal to 660 nm.

3. The device according to claim 1 or 2, wherein the measurement light generation element is a laser transmitter.

4. The device according to claim 3, wherein the laser transmitter outputs light within the red spectral region.

5. The device according to any preceding claim, wherein the device is configured to calculate the blood glucose level measurement using an equation derived by a supervised machine learning model.

6. The device according to claim 5, wherein the supervised machine learning model is trained on a dataset containing a plurality of historic blood glucose level measurements measured invasively and respective digit depths, digit characteristic parameters and transmission indices.

7. The device according to any preceding claim, wherein the digit characteristic parameter unit comprises an input module, the input module configured to receive input of a digit characteristic parameter from an operator of the blood glucose level sensing device.

8. The device according to any preceding claim, further comprising a temperature sensor configured to measure a temperature of the digit; andwherein the blood glucose level sensing device is configured to determine a blood glucose level measurement further based on the digit temperature.

9. The device according to any preceding claim, further comprising a vibration sensor configured to measure an acceleration of the sensing device during transmission measurement; and wherein the light-transmission measurement unit is configured to adjust a voltage based on said acceleration.

10. The device according to any preceding claim, further comprising a fingerprint sensor.11 . The device according to any preceding claim, wherein the digit-depth measurement unit comprises: a displaceable member configured to be displaced in a first direction by the digit; and a time-of-flight sensor module configured to measure the displacement of the displaceable member in the first direction.

12. The device according to any preceding claim, further comprising a communications unit configured to connect to a network for transmission of the blood glucose value.

13. The device according to any preceding claim, further comprising a calibration unit, wherein the calibration unit is configured to: receive an initial blood glucose level measurement of the subject performed by the sensing device; receive a reference blood glucose level measurement of the subject; and determine a calibration factor for the subject by comparing the initial blood glucose level measurement to the reference blood glucose measurement; wherein the sensing device is configured to determine one or more future blood glucose level measurements further based on the calibration factor.

14. A blood glucose monitoring system comprising: a blood glucose level sensing device according to any one of claims 1 to 13; and an analysis device; and wherein: the blood glucose level sensing device is connectable to the analysis device to provide the analysis device with a plurality of historical blood glucose values pertaining to a subject; and the analysis device is configured to determine a risk factor representing the risk of the subject developing diabetes based on the plurality of blood glucose values.

15. A method of non-invasively determining a blood glucose level of a subject via a digit of the subject, the method comprising the steps of: measuring or receiving a depth of the digit in a first direction;directing a measurement light through the digit in the first direction; measuring a transmission index representing the proportion of the measurement light transmitted through the digit; determining one or more digit characteristic parameters, each digit parameter indicative of: a skin tone of the digit; a nail texture of the digit; a nail thickness of the digit; a nail length of the digit; or a nail polish status of the digit; and determining a blood glucose level measurement based on the depth of the digit, the transmission index and at least one of the digit characteristic parameters.

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