Compensation system and method for thermistor sensing in an analyte biosensor

Abstract

An analyte concentration sensor system selects a temperature for input to an analyte concentration estimation algorithm. The analyte concentration estimation algorithm is executed by an analyte meter that analyzes a sample in a test sensor. A thermistor-based temperature sensor is configured to measure a temperature. An estimated temperature is obtained by a temperature estimation algorithm. A difference between the estimated temperature and the measured temperature is determined. One of the estimated temperature and the measured temperature is selected based on the estimated temperature, the measured temperature, and an absolute difference between the estimated temperature and the measured temperature. Additionally, a fault in the test sensor can be determined based on the estimated temperature, the measured temperature, and the absolute difference between the estimated temperature and the measured temperature.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority and benefit to U.S. Provisional Patent Application No. 62 / 850,841, filed May 21, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention generally relates to a biosensor for analyte concentration (e.g., blood glucose), and more specifically to a system for detecting test sensor malfunctions when providing a temperature value of an estimated temperature or a measured temperature from the analyte concentration determination process. Background Technology

[0004] The quantitative determination of analytes in body fluids is crucial in the diagnosis and maintenance of certain physiological conditions. For example, patients with diabetes mellitus (PWD) frequently have their glucose levels in body fluids checked. The results of such tests can be used to adjust their dietary glucose intake and / or determine whether insulin or other medications are needed. PWD patients typically use measuring devices (e.g., blood glucose meters) to calculate the glucose concentration in fluid samples collected from the fluid sample and received by the measuring device. Without correction, this can have serious medical consequences for the patient.

[0005] One method for monitoring blood glucose levels in patients with PWD is to use portable testing devices. The portability of these devices allows users to conveniently test their blood glucose levels anywhere. One type of device utilizes an electrochemical testing sensor to analyze blood samples. The user uses a lancet to obtain a blood sample and applies it to a reservoir in the testing sensor. The electrochemical testing sensor typically includes electrodes that, when used with an instrument, electrically measure the reaction of the blood sample to determine the analyte concentration. Therefore, the user must carry specialized instrumentation to interpret the blood sample analysis.

[0006] Typically, instruments apply an input signal (e.g., a gated amperometry signal) to the electrodes of the test sensor. Traditional test sensors and instruments often use glucose concentration estimation algorithms that determine the correlation between the measured current output from the blood sample and a predetermined analyte concentration value associated with such output. These predetermined values ​​are determined by laboratory instruments such as YSI laboratory instruments.

[0007] The chemical reactions employed in the test sensors of any amperometric blood glucose monitoring (BGM) system are affected by temperature. Therefore, measuring the temperature value is an important input to the glucose estimation algorithm of such systems. In known systems, the temperature is measured by a thermistor-based temperature sensor. The thermistor of the temperature sensor is typically located within the meter. Due to the thermal mass of the meter, the thermistor is unable to respond immediately to changes in the ambient temperature and therefore the temperature measurement can be distorted. When a BGM meter is moved from one environment to another, the meter requires a period of time to equilibrate with the new environment, during which time the thermistor value will not accurately reflect the actual temperature. In the complex glucose estimation algorithm employed in gated amperometric meters, the temperature is included in many of the terms in various compensation equations, so when the thermistor-based temperature value is incorrect, incorrect results can occur.

[0008] Therefore, there is a risk that the temperature estimate from the thermistor is not from an environment to which the meter has equilibrated, which in turn causes the algorithm to use an incorrect temperature value. This creates a risk of inaccurate glucose readings. One solution to the non-equilibrated environment is to use an estimated temperature based on other parameters that are not obtained from the thermistor. However, using an estimated temperature creates another risk from a damaged sensor, which can produce an incorrect temperature estimate. Therefore, in addition to a non-equilibrated meter, a large difference between the estimated temperature and the thermistor can indicate a damaged sensor. In the case of a damaged sensor, the correct response is to report an error code. However, if a damaged sensor is not detected, the meter can attempt to use the temperature measurement from the damaged sensor to calculate glucose, which can result in inaccurate glucose readings.

[0009] Therefore, there is a need for a process to address the risk of inaccurate glucose results from a non-equilibrated meter that relies solely on thermistor-based temperature measurements. There is also a need for a system that compares an estimated temperature to a measured temperature to provide information about whether the meter is properly equilibrated. There is also a need for a system that can use an estimated temperature from a temperature estimation algorithm to determine an analyte concentration even when a non-equilibrated is detected. There is also a need for a system that compares an estimated temperature to a measured temperature to provide information about whether a test sensor is damaged. SUMMARY

[0010] According to one example, an analyte concentration sensor system for measuring an analyte of a fluid sample of a user is disclosed. The sensor system includes a biosensor interface operable to connect to a test sensor containing the fluid sample. A thermistor-based temperature sensor is structured to measure a temperature. A controller is coupled to the biosensor interface and the temperature sensor. The controller is operable to generate an input signal input to the biosensor interface and read an output signal from the biosensor interface. The controller determines a measured temperature from the temperature sensor. The controller executes a temperature estimation algorithm to determine an estimated temperature. The controller determines a difference between the estimated temperature and the measured temperature. The controller selects one of the estimated temperature and the measured temperature based on the estimated temperature, the measured temperature, and the difference between the estimated temperature and the measured temperature. The controller provides the selected estimated temperature or measured temperature as a temperature input to an analyte concentration determination algorithm.

[0011] Another example is a method for determining the suitability of a temperature measurement of a thermistor temperature sensor in an analyte meter, the analyte meter including a biosensor interface and a controller, the biosensor structure operable to connect to a test sensor containing a fluid sample. An input signal is generated to the interface when connected to the test sensor with the fluid sample. An output signal from the test sensor is determined. A measured temperature from a thermistor-based temperature sensor is determined. An estimated temperature is determined by a temperature estimation algorithm by the controller. A difference between the estimated temperature and the measured temperature is determined by the controller. One of the estimated temperature and the measured temperature is selected by the controller based on the estimated temperature, the measured temperature, and the difference between the estimated temperature and the measured temperature. The selected estimated temperature or the measured temperature is provided as a temperature input to an analyte concentration determination algorithm.

[0012] Another example is an analyte concentration sensor system for measuring an analyte of a fluid sample of a user. The sensor system includes a biosensor interface operable to connect to a test sensor containing a fluid sample. The system includes a thermistor-based temperature sensor configured to measure a temperature. The system includes a controller coupled to the biosensor interface and the temperature sensor. The controller is operable to generate an input signal to the biosensor interface and read an output signal from the biosensor interface. The controller is operable to determine a measured temperature from the temperature sensor and execute a temperature estimation algorithm to determine an estimated temperature. The controller determines an absolute difference between the estimated temperature and the measured temperature. The controller determines a failure of the test sensor based on the estimated temperature, the measured temperature, and the absolute difference between the estimated temperature and the measured temperature.

[0013] Another example is a method for determining a failure of a test sensor connected to an analyte meter. The analyte meter includes a biosensor interface operable to connect to the test sensor containing a fluid sample and a controller. An input signal is generated to the interface when connected to the test sensor with the fluid sample. An output signal from the test sensor is determined. A measured temperature from a thermistor-based temperature sensor is determined. An estimated temperature is determined by a temperature estimation algorithm by the controller. An absolute difference of the estimated temperature and the measured temperature is determined by the controller. A failure of the test sensor is determined based on the estimated temperature, the measured temperature, and the absolute difference of the estimated temperature and the measured temperature.

[0014] Other aspects of the application will become apparent to those of ordinary skill in the art upon reading the following detailed description in conjunction with the drawings, in which: BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a block diagram of an exemplary biosensor system for determining an analyte concentration from a fluid sample according to one embodiment;

[0016] Figures 2A-2B is a flowchart of a procedure executed by a biosensor in Figure 1 for selecting a temperature value to use in an analyte concentration estimation algorithm;

[0017] Figure 3 is a state diagram of a response of the procedure in Figures 2A-2B which shows a state of using a measured temperature, using an estimated temperature, or returning an error message;

[0018] Figure 4 Parameter table that is an example of a temperature estimation algorithm;

[0019] Figure 5A Summary table of outputs of temperature estimation algorithms compared to temperatures measured by thermistor-based sensors;

[0020] Figure 5B Summary table of outputs of analyte concentration estimation algorithms using temperatures measured by thermistor-based sensors and outputs of temperature estimation algorithms for research performed by meters in equilibrium states;

[0021] Figure 6 Graph of an exemplary input signal sequence to a temperature estimation algorithm;

[0022] Figure 7A Plot of errors in outputs of analyte concentration estimation algorithms using measured temperatures from tests performed by meters in a wide range of equilibrium states;

[0023] Figure 7B Plot of errors in outputs of analyte concentration estimation algorithms using estimated temperatures from tests performed by meters in a wide range of equilibrium states;

[0024] Figure 8 Plot of errors in outputs of analyte concentration estimation algorithms using final selected temperatures (either estimated or measured) from tests performed by meters in a wide range of equilibrium states;

[0025] Figure 9 Summary table of output accuracy of analyte concentration estimation algorithms for tests performed by meters in three equilibrium states (cold, hot, and equilibrium) comparing results calculated using the following temperatures, i.e., temperatures measured by thermistor-based sensors, temperatures estimated using algorithms from signals from test sensors, and temperatures selected by logic based on differences between thermistor and estimated temperatures.

[0026] While the application is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the application is not to be limited to the particular DETAILED DESCRIPTION

[0027] The present disclosure relates to an analyte concentration measurement system that employs temperature balancing logic to estimate ambient temperature using a non-thermistor signal. The difference between the estimated temperature and the temperature measured from the thermistor is compared to a predetermined threshold to determine which of three actions to perform. The three actions include: 1) normally calculating analyte concentration using the thermistor signal assuming the meter is balanced and the test sensor signal is valid; 2) calculating analyte concentration using the estimated temperature assuming the meter is not balanced to ambient conditions and the estimated temperature will yield a more accurate result; or 3) reporting an error assuming the test sensor is damaged and the signal is invalid.

[0028] The logic controlling the three possible actions is as follows. When the estimated temperature and the measured temperature of the thermistor are in sufficient agreement, the results of both are assumed to be accurate and analyte concentration is calculated using the measured temperature of the thermistor as it produces the most reliable value under normal circumstances. When a large discrepancy between the thermistor and the estimated temperature is observed, there are two possible explanations: 1) the thermistor measured temperature is inaccurate because the meter is not balanced to the surrounding environment; or 2) the estimated temperature is inaccurate because the sensor signal used to calculate the sensor is incorrect (caused by sensor damage or perturbation of the sample during the test). The decision whether to report a corrected result or an error message is based on an understanding of which of the two possible cases is most likely given the relationship between the thermistor measured temperature and the estimated temperature. Since most glucose concentration tests are performed at room temperature, when the thermistor measured temperature is at an extreme but the estimated temperature is normal, imbalance is the most likely explanation and analyte concentration is calculated using the estimated temperature. When the temperature reading of the thermistor is normal but the estimated temperature is at an extreme, it is more likely that the signal output waveform of the test sensor is abnormal and therefore an error should be reported.

[0029] Figure 1 A schematic diagram of a biosensor system 100 for determining analyte concentration in a biological fluid sample is shown. The biosensor system 100 includes a measurement device 102 and a test sensor 104, which can be implemented in any analytical instrument including a benchtop device, a portable or handheld device, or the like. The measurement device 102 and the test sensor 104 can be adapted to implement an electrochemical sensor system, an optical sensor system, or a combination thereof, among others. The biosensor system 100 utilizes a glucose estimation algorithm to determine analyte concentration from an output signal, which uses a temperature input to correct its output for temperature. A temperature selection procedure determines whether to use a temperature measured from a thermistor sensor, an estimated temperature, or to return an error message. As will be explained, this procedure improves the measurement performance of the biosensor system 100 in determining analyte concentration of a sample by providing a more accurate temperature input to the analyte concentration estimation algorithm.

[0030] The biosensor system 100 can be used to determine analyte concentrations, including glucose, lipid profiles (e.g., cholesterol, triglycerides, LDL, and HDL), microalbumin, hemoglobin Al C Fructose, lactate, or bilirubin concentrations. Other analyte concentrations are contemplated to be determined as well. More than one analyte is contemplated to be determined as well. The analytes can be in, for example, whole blood samples, serum samples, plasma samples, other bodily fluids such as urine, and non-bodily fluids. Thus, one example of an analyte concentration estimation algorithm is a glucose concentration estimation algorithm performed by the biosensor system 100. As used in this application, the term "concentration" refers to an analyte concentration, activity (e.g., enzymes and electrolytes), titer (e.g., antibodies), or any other measured concentration used to measure a desired analyte. Although a particular configuration is shown, the biosensor system 100 can have other configurations, including configurations with additional components.

[0031] The test sensor 104 has a base 106 that forms a reservoir 108 and a channel 110 with an opening 112. The reservoir 108 and channel 110 can be covered by a lid with a vent. The reservoir 108 defines a partially enclosed volume. The reservoir 108 can contain a composition that aids in containing a liquid sample, such as a water- swellable polymer or a porous polymer matrix. Reagents can be deposited in the reservoir 108 and / or channel 110. The reagents can include one or more enzymes, adhesives, mediators, etc. The reagents can include a chemical indicator for an optical system. The test sensor 104 can also have a sample interface 114 disposed adjacent to the reservoir 108. The sample interface 114 can partially or completely surround the reservoir 108. The test sensor 104 can have other configurations.

[0032] In an optical sensor system, the sample interface 114 has an optical portal or aperture for viewing the sample. The optical portal can be covered by a substantially transparent material. The sample interface can have an optical portal on both sides of the reservoir 108.

[0033] In an electrochemical system, the sample interface 114 has conductors connected to a working electrode and a counter electrode. The electrodes can be substantially in the same plane or in different planes. The electrodes can be disposed on a surface of the base 106 that forms the reservoir 108. The electrodes can extend into or protrude into the reservoir 108. A dielectric layer can partially cover the conductors and / or electrodes. The sample interface 114 can have other electrodes and conductors.

[0034] The measurement device 102 includes circuitry 116 connected to the sensor interface 118 and a display 120. The circuitry 116 includes a processor 122 connected to a signal generator 124, a temperature sensor 126, and a storage medium 128. In the present example, the temperature sensor 126 operates by providing an electrical signal to a thermistor and reading an output signal from the thermistor that is proportional to the ambient temperature.

[0035] The signal generator 124 provides an electrical input signal to the sensor interface 118 in response to the processor 122. In optical systems, the electrical input signal can be used to operate or control a detector and a light source in the sensor interface 118. In electrochemical systems, the electrical input signal can be transmitted by the sensor interface 118 to the sample interface 114 to apply the electrical input signal to a sample of biological fluid. The electrical input signal can be a potential or a current and can be constant, variable, or a combination thereof, such as an AC signal applied with a DC signal offset. The electrical input signal can be applied in a single pulse or multiple pulses, a sequence, or a cycle, such as a gated current measurement signal. The signal generator 124 can also record output signals from the sensor interface as a generator-recorder.

[0036] The temperature sensor 126 determines the temperature of the sample in the reservoir of the test sensor 104 based on the output signal of the thermistor in the sensor 126. As will be explained below, the temperature of the sample can be estimated by a calculation from a non-temperature signal (e.g., an output signal or signals, time, a ratio between signals, etc.). The estimated temperature is assumed to be the same or similar to a measured value of the ambient temperature or a temperature of the device implementing the biosensor system. Another temperature sensing device can be used to measure the temperature.

[0037] The storage medium 128 can be a magnetic storage, an optical storage, or a semiconductor storage, other storage devices, etc. The storage medium 128 can be a fixed storage device, a removable storage device such as a memory card, a remotely accessed storage device, etc.

[0038] The processor 122 uses computer readable software code and data stored in the storage medium 128 to implement analyte analysis and data processing. The processor 122 can initiate analyte analysis in response to the presence of a test sensor 104 at the sensor interface 118, sample being applied to the test sensor 104, in response to user input, etc. The processor 122 instructs the signal generator 124 to provide one or more electrical input signals to the sensor interface 118. The processor 122 receives an output signal related to sample temperature from the temperature sensor 126. The processor 122 receives one or more output signals from the sensor interface 118. The output signal is generated in response to a reaction of an analyte in the sample. The output signal can be generated using an optical system or an electrochemical system, etc. The processor 122 determines a compensated analyte concentration from the output signal using the glucose estimation algorithm discussed previously. The results of the analyte analysis can be output to the display 120 and can be stored in the storage medium 128.

[0039] The correlation equation between analyte concentration and output signal can be represented in graphical, mathematical, and combinations thereof, etc. The correlation equation can include one or more exponential functions. The correlation equation can be represented by a program number (PNA) table or other look-up table stored in the storage medium 128, etc. Constants and weighting factors can also be stored in the storage medium 128. Instructions for implementing analyte analysis can be provided by computer readable software code stored in the storage medium 128. The code can be object code or any other code describing or controlling the functions described herein. Data from the analyte analysis can be subjected to one or more data processing in the processor 122, including determining decay rates, K constants, ratios, functions, etc. In this example, the storage medium 128 stores an analyte concentration estimation algorithm 130 that determines an analyte concentration from inputs such as signals from the sensor interface 118, etc. The storage medium also stores a temperature selection program 132 that determines a temperature value for input to the analyte concentration estimation algorithm 130. The storage medium 128 also stores a temperature estimation algorithm 134 for determining an estimated temperature value for use by the temperature selection program 132.

[0040] In an electrochemical system, the sensor interface 118 has contacts that are connected or in electrical communication with conductors in the sample interface 114 of the test sensor 104. The sensor interface 118 transmits electrical input signals from the signal generator 124 to the connectors in the sample interface 114 through the contacts. The sensor interface 118 also transmits output signals from the sample to the processor 122 and / or the signal generator 124 through the contacts.

[0041] In a light absorption and light generation optical system, the sensor interface 118 includes a detector that collects and measures light. The detector receives light from the liquid sensor through an optical portal in the sample interface 114. In a light absorption optical system, the sensor interface 118 also includes a light source such as a laser, a light emitting diode, or the like. The incident light beam can have a wavelength selected for absorption by a reaction product. The sensor interface 118 passes the incident light beam from the light source through the optical portal in the sample interface 114. The detector can be placed at an angle, for example 45°, from the optical portal to receive light reflected back from the sample. The detector can be disposed near the optical portal on the other side of the sample from the light source to receive light transmitted through the sample. The detector can be located in other positions to receive reflected light and / or transmitted light.

[0042] The display 120 can be analog or digital. The display 120 can include an LCD, LED, OLED, vacuum fluorescent lamp, or other display suitable for displaying a digital reading. Other displays can be used. The display 120 is in electrical communication with the processor 122. The display 120 can be separate from the measurement device 102, for example when in wireless communication with the processor 122. Alternatively, the display 120 can be removed from the measurement device 102, for example when the measurement device 102 is in electrical communication with a remote computing device, a medication dosing pump, or the like.

[0043] In use, a liquid sample for analysis is delivered into the reservoir 108 by introducing the liquid into the opening 112. The liquid sample flows through the channel 110, filling the reservoir 108 while expelling previously contained air. The liquid sample chemically reacts with reagents deposited in the channel 110 and / or the reservoir 108.

[0044] The test sensor 104 is disposed adjacent to the measurement device 102. "Adjacent" includes positions in which the sample interface 114 is in electrical and / or optical communication with the sensor interface 118. Electrical communication includes the transmission of input and / or output signals between contacts in the sensor interface 118 and conductors in the sample interface 114. Optical communication includes the transmission of light between an optical portal in the sample interface 114 and a detector in the sensor interface 118. Optical communication also includes the transmission of light between an optical portal in the sample interface 114 and a light source in the sensor interface 118.

[0045] The processor 122 receives a measured temperature from the temperature sensor 126. The processor 122 instructs the signal generator 124 to provide an input signal to the sensor interface 118. In an optical system, the sensor interface 118 operates the detector and the light source in response to the input signal. In an electrochemical system, the sensor interface 118 provides the input signal to the sample through the sample interface 114. The processor 122 receives an output signal generated in response to the redox reaction of an analyte in the sample as previously described.

[0046] In this example, the processor 122 determines the analyte concentration of the sample by an analyte concentration estimation algorithm 130. One of the inputs to the analyte concentration estimation algorithm 130 is the temperature, which is used to correct for the effects of temperature differences on the sensor output signal.

[0047] The processor 122 in this example can operate to execute a temperature selection procedure 132 that selects the temperature for the analyte concentration estimation algorithm 130. The processor 122 also executes a temperature estimation algorithm 134 that is capable of estimating the ambient temperature with sufficient accuracy that such an estimated ambient temperature can reliably detect an imbalance and be used by the analyte concentration estimation algorithm 130 to compute accurate results. The temperature selection procedure 132 also includes logic to determine when a large difference between the estimated temperature and the temperature measured by the thermistor of the temperature sensor 126 is caused by a damaged sensor rather than an imbalance, thereby enabling an error code to be displayed on the display rather than an erroneous result resulting from performing the analyte concentration estimation algorithm 130 using the temperature output of a damaged temperature sensor. Alternatively, the error code can refer to an error index number or refer to actual information displayed on the display 120 and / or recorded in memory.

[0048] Figures 2A-2B is a flowchart showing Figure 1 the temperature selection procedure 132 in the example biosensor system 100 that determines the temperature value input to the analyte concentration algorithm 130. The procedure 132 is executed on a controller such as the processor 122 in Figure 1 Although it would be better to use the estimated temperature when the thermistor offset exceeds 3°C, it is not possible to know for certain when this actually occurs. The only information available to the temperature selection procedure 132 is the difference between the thermistor and the estimated temperature. Therefore, Figures 2A-2B the temperature selection procedure 132 in follows certain temperature compensation logic to determine whether to use the estimated temperature, the temperature from the thermistor, or to return an error message.

[0049] The procedure 132 first measures all of the test signals (200). This includes applying the input signals from the signal generator 124 to the electrodes in the test sensor 104. The processor 122 reads the output signals from the sensor interface 118. The test signal measurement step also includes the processor 122 reading the signal from the temperature sensor 126 in Figure 1 and determining the measured ambient temperature (T). The processor 122 estimates the ambient temperature (T Est) based on the output signals read from the sensor interface 118 and other inputs required by the temperature estimation algorithm 134 (202). The processor 122 then determines the absolute value of the difference between the estimated ambient temperature and the temperature measured by the temperature sensor 126 (T Est Residual) (204).

[0050] The processor 122 then determines whether the absolute value of the difference between the estimated ambient temperature and the temperature measured by the temperature sensor 126 exceeds a maximum allowed temperature compensation value (MaxComp) (206). If the difference exceeds the maximum allowed temperature compensation, the processor 122 reports an error code for the test sensor 104 (208). In this example, the maximum variation between the estimated temperature and the temperature measured from the sensor 126 is 22°C, although other values can be used, such as between 15°C and 25°C. Such a large difference indicates that the system 100 is unlikely to be in a true unbalanced state, so it is safer to report an error code indicating that the test sensor 104 is malfunctioning.

[0051] If the difference is below the maximum allowed temperature compensation value, the processor 122 then determines whether both the measured temperature from the temperature sensor 126 and the estimated temperature are within a room temperature range (210). In this example, the room temperature range is between 17.5°C and 27.5°C (e.g., 22.5 ± 5°C), although other range values can be used. For example, the room temperature range can be defined differently depending on the expected typical use environment. Thus, the high temperature of the room temperature range can be between 25°C and 30°C, and the low temperature can be between 13°C and 20°C. If both the estimated temperature and the measured temperature are outside the room temperature range and in opposite directions, the processor 122 then reports an error code for the test sensor 104 (208).

[0052] If both the temperature and the estimated temperature are within the room temperature range, the processor 122 determines whether the measured temperature is within the room temperature range and whether the difference between the measured temperature and the estimated temperature is greater than a residual limit threshold (212). If the measured temperature is within the room temperature range, but the difference between the measured temperature and the estimated temperature is greater than the residual limit threshold, the processor 122 reports an error code for the test sensor 104 (208). In this example, the residual limit threshold is 10°C, and a difference above 10°C indicates that the test sensor is damaged, so an error code is reported. The residual limit threshold can range between 7°C and 15°C, depending on the system.

[0053] If the difference is less than the residual limit threshold, the processor 122 determines whether both the temperature and the estimated temperature are greater than the high temperature of the room temperature range and whether the difference between the estimated temperature and the measured temperature is greater than a limit residual limit threshold (214). If these conditions are met, the processor 122 reports an error code for the test sensor 104 (208). In this example, the high temperature of the room temperature range is 27.5°C, and the limit residual limit threshold is 12°C.

[0054] If these conditions are not met, the processor 122 determines whether both the measured temperature and the estimated temperature are less than the lower temperature of the room temperature range and whether the difference between the measured temperature and the temperature estimate is greater than the extreme residual limit threshold (216). In this example, the lower temperature of the room temperature range is 17.5 °C and the extreme residual limit threshold for steps 214 and 216 is 12 °C. The extreme residual limit threshold can range between 7 °C and 15 °C for steps 214 and 216 depending on the system. If these conditions are met, the processor 122 reports an error code for the test sensor 104 (208). In this example, the extreme residual limit threshold is slightly wider than the residual limit threshold because the estimated temperature can be slightly less reliable in extreme conditions. However, in some examples, the same value can be used for both thresholds.

[0055] If the above conditions are not met, the processor 122 determines whether: a) the measured temperature is less than the lower temperature of the temperature range and the estimated temperature is greater than or equal to the low adjusted temperature value; or b) the measured temperature is greater than the upper temperature of the room temperature range and the estimated temperature is less than or equal to the high adjusted temperature value (218). This step determines whether the temperature measured by the thermistor is an extreme when the estimated temperature is at room temperature, a combination that is consistent with an imbalanced meter that has recently been brought from a hot or cold environment. When a meter is imbalanced, a small amount of heat is transferred into or out of the sensor, causing the expected temperature of a sensor tested in a hot meter to shift up and the expected temperature of a sensor tested in a cold meter to shift down. In this example, the high adjusted temperature value is 2.5 °C higher than the high temperature value of the room temperature range and the low adjusted temperature value is 2.5 °C lower than the low temperature value of the room temperature range, so the low adjusted temperature value is 15 °C and the high adjusted temperature value is 30 °C. If these conditions are not met, the processor 122 uses the temperature from the temperature sensor 126 as the temperature input to the analyte concentration estimation algorithm 130 (220).

[0056] If the conditions in step 218 are met, the processor 122 compares the absolute difference between the measured temperature and the estimated temperature to a threshold balance value (222). In this example, the threshold balance value is 6 °C. The 6 °C threshold balance value of the example can be adjusted depending on the accuracy of the temperature estimation algorithm and the desired risk balance between false negative and false positive results. The threshold balance value can range between 3 °C and 10 °C. If the difference is greater than the threshold balance value, the processor 122 uses the estimated temperature as the temperature input to the analyte concentration algorithm 130 (224). If the absolute difference is less than the threshold balance value, the processor 122 uses the temperature from the temperature sensor 126 as the temperature input to the analyte concentration estimation algorithm 130 (222).

[0057] Figure 3is a plot showing the correlation between the estimated temperature and the measured temperature from the temperature sensor and the different logic states as a result. The first region 300 represents the case where the measured temperature is used for the temperature input to the analyte concentration estimation algorithm 130. The two regions 310 and 312 represent the case where the estimated temperature is used for the temperature input to the analyte concentration estimation algorithm 130. The regions 310 and 312 are bounded by the lines 302 and 304 representing the room temperature range boundaries. The regions 310 and 312 are further bounded by the lines 314 and 316 representing the lower bounds of the equilibrium boundaries. The two additional regions 320 and 322 represent the case where an error message is returned to indicate that the temperature sensor 126 has been damaged.

[0058] In this example, the estimation of temperature is determined by a temperature estimation algorithm 134. The temperature estimation algorithm 134 is derived from a multiple regression analysis of the input variables. Such an algorithm can be developed by performing a multiple regression based on different parameters for a particular test sensor and other measured signals. In this example, a multiple regression equation was developed that accurately estimates the ambient temperature (1.5 °C standard deviation) using the electrical signals produced by the test sensor during a glucose test.

[0059] An equation with different terms of the parameters shown in the table in Figure 4 was developed using training data from a large database of current profiles taken from properly equilibrated meters tested under a wide range of conditions. The accuracy of this temperature estimation algorithm was evaluated by a set of 38,367 laboratory study readings and 12,796 internal clinical study readings obtained from normally filled sensors tested with equilibrated meters. The summary statistics of the comparison between the temperature measured by the temperature sensor and the output of the example temperature estimation algorithm are included in the table shown in Figure 5A . Figure 5B A summary table showing the error percentage of glucose results calculated using the thermistor and using the estimated temperature from the equilibrated meter is shown. Although the temperature estimation algorithm is accurate, using this estimate when the meter is equilibrated and the thermistor is correct results in slightly worse performance.

[0060] In this example, the equation for estimating the temperature in °C includes a number of terms based on the parameters in Figure 4 and a constant. The temperature estimate is calculated as the sum of these terms and the constant. The signals are measured during six potential pulses at the main glucose working electrode (M pulses) and four potential pulses at the bare "G" electrode in front of the test strip test chamber (G pulses). At the end of the test, a single high potential pulse is applied to the G electrode to measure a signal related to the hematocrit (H pulse). This potential input signal sequence pattern is shown in Figure 6 . Figure 6 A sequence of six main pulses 610, 612, 614, 616, 618, and 620 is shown.Figure 6 Four pulses 630, 632, 634, and 636 at the bare G electrode are shown. Figure 6 Input signals 640 used to measure signals related to hematocrit are also shown.

[0061] The current signals measured during one of the six M pulses are designated MxArray(y), where x is the pulse number (1-6) and y is the number of measurements within the pulse. The four G pulses (i.e., GxArray(y)) use the same conditions. Four signals are measured during a single H pulse: HArray(y). The parameters in the shown table. Each term in the estimation equation is the product of a coefficient and an indicator parameter constructed from one or more measured current values. Figure 4

[0062] Of course, other procedures for determining the temperature estimate can be used, such as through an artificial neural network with appropriate machine learning algorithms. In this example, the temperature estimation algorithm 134 provides accurate results in studies representing a wide range of temperatures, glucose concentrations, and hematocrit levels.

[0063] Three studies were performed with meters that were stored at cold or hot temperatures, and then tested at room temperature (~22°C). For out-of-balance meters, the results calculated using the incorrect thermistor value are inaccurate, especially when the meter is colder than the test environment. However, the results calculated with the estimated temperature are accurate in all cases. Therefore, it is highly desirable to successfully identify when a meter is out-of-balance, and then use the estimated temperature instead of the measured temperature to calculate glucose. Figure 7A is a plot of the error in the output of an analyte concentration estimation algorithm using the measured temperature from tests performed with meters at a wide range of in-balance states. Figure 7B is a plot of the error in the output of an analyte concentration estimation algorithm using the estimated temperature from tests performed with meters at a wide range of in-balance states. Figure 8 is a plot of the error in the output of an analyte concentration estimation algorithm using the final selected temperature (either the estimated temperature or the measured temperature) from tests performed with meters at a wide range of in-balance states. In this case, the error is calculated as the absolute value of the difference between the true glucose concentration and the estimated glucose concentration. Figures 7A-7B and Figure 8 In the plots in and, the “*” symbol represents output from a hot meter, the “o” symbol represents output from an in-balance meter, and the “x” symbol represents output from a cold meter.

[0064] Figures 7A-7B shows that when a meter is actually out-of-balance, the glucose results calculated with the estimated temperature are much more accurate than the glucose results calculated with the thermistor. Figure 8 shows that the algorithm logic works well and correctly switches to the estimated temperature when a severe imbalance occurs, thus preventing Figure 7A ​the severe inaccuracies seen in the middle.

[0065] Application of the unbalance logic can significantly improve performance for meters that are not balanced after being brought back from a cold or hot environment, while maintaining performance for balanced meters. Figure 9 The results of the study for balancing meters, cold meters, and hot meters related to the temperature selection procedure 132 in FIG. 13 are shown in the summary data table. Figures 2A-2B The results of the study for balancing meters, cold meters, and hot meters related to the temperature selection procedure 132 in FIG. 13 are shown in the summary data table.

[0066] As described above, in addition to unbalanced meters, the temperature selection procedure 132 is also able to determine a damaged test sensor and thus avoid using data from a damaged test sensor for analyte concentration. There have been many studies on damaged or interfered test sensors. Such damaged test sensors produce abnormal current signals, thus affecting the accuracy of temperature estimation. The temperature selection procedure 132 thus determines whether the difference between the estimated temperature and the measured temperature is greater than a threshold level, and likely due to an error in the estimated temperature rather than the measured temperature, thus indicating an error from the test sensor. Thus, this difference is used as an error detection tool for test sensor failure.

[0067] This logic greatly improves the performance of meters that are not balanced in practice, while also improving the error detection success rate when test sensor damage occurs, and maintaining current performance when the test sensor is normal.

[0068] As used in this application, the terms "component," "module," "system" and the like are generally intended to refer to a computer-related entity, either hardware (e.g., a circuit), a combination of hardware and software, software, or an entity related to an operational machine with one or more specific functionalities. For example, a component can be, but is not limited to being, a process running on a processor (e.g., a digital signal processor), a processor, an object, an executable, a thread of execution, a program, and / or a computer. By way of illustration, both an application running on a controller and the controller can be a component. One or more components can reside within a process and / or thread of execution and a component can be localized, co-resident, and / or distributed among one or more computer(s) and / or processes and / or threads of execution. Also, a "device" can take many forms, including a specially designed hardware form that is dedicated to a specific function; general-purpose hardware that is specially configured through the execution of software that enables the hardware to perform a specific function; software stored on a computer-readable medium that, when executed, causes a general-purpose computer to become a specialized machine configured to perform a specific function; or a combination of these.

[0069] While the application has been illustrated and described in relation to one or more embodiments, equivalent changes and modifications in the implementation can become apparent to those skilled in the art after reading and understanding the specification and the appended drawings. Furthermore, while the particular features of the application can have been disclosed in only one of the various embodiments, such features can be combined with one or more other features of the other embodiments as to an embodiment or to combinations of portions of different embodiments as can be desired and advantageous for any given or particular application or uses.

Claims

1. An analyte concentration sensor system for measuring analytes in a user's fluid sample, the sensor system comprising: A biosensor interface, operable to connect to a test sensor containing the fluid sample; A temperature sensor based on a thermistor, the temperature sensor being configured to measure temperature; A controller, coupled to the biosensor interface and the temperature sensor, is operable to: Generate an input signal that is fed into the biosensor interface; Read the output signal from the biosensor interface; Determine the measured temperature from the temperature sensor; Execute a temperature estimation algorithm to determine the estimated temperature; Determine the absolute value of the difference between the estimated temperature and the measured temperature; Choose one of the estimated temperature and the measured temperature, the selection being based on the estimated temperature, the measured temperature, and the absolute value of the difference between the estimated temperature and the measured temperature; The selected estimated temperature or the measured temperature is provided as the temperature input for the analyte concentration determination algorithm; The analyte concentration is determined by executing the analyte concentration determination algorithm. as well as If the absolute value of the difference between the estimated temperature and the measured temperature is greater than the maximum allowable temperature compensation value, then an error code for the test sensor is reported.

2. The sensor system as described in claim 1, wherein, The analyte is glucose and the fluid sample is blood.

3. The sensor system as described in claim 1, wherein, The input signal is a gate control current analysis pulse.

4. The sensor system as described in claim 1, wherein, The temperature estimation algorithm includes input variables determined by multiple regression analysis.

5. The sensor system as described in claim 1, wherein, If the estimated temperature and the measured temperature are within the room temperature range, then the measured temperature is selected.

6. The sensor system as described in claim 5, wherein, The room temperature range includes high temperatures between 25°C and 30°C and low temperatures between 13°C and 20°C.

7. The sensor system as claimed in claim 1, wherein, If the measured temperature is outside the room temperature range, but the estimated temperature is less than the adjusted high temperature of the room temperature range and greater than the adjusted low temperature of the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the equilibrium threshold, then the estimated temperature is selected.

8. The sensor system of claim 7, wherein, The room temperature range includes a high temperature between 25°C and 30°C and a low temperature between 13°C and 20°C, wherein the adjusted high temperature is between 27°C and 34°C, the adjusted low temperature is between 11°C and 18°C, and the equilibrium threshold is between 3°C and 10°C.

9. The sensor system as claimed in claim 1, wherein, If the measured temperature and the estimated temperature are outside the room temperature range in opposite directions, the controller is able to operate to report a second error code for the test sensor.

10. The sensor system of claim 1, wherein, If the measured temperature is within the room temperature range and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the residual limit threshold, the controller is able to operate to report a second error code for the test sensor.

11. The sensor system of claim 10, wherein, If the measured temperature and the estimated temperature are both higher than the highest temperature in the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the limit residual threshold, then the controller is able to operate to report a third error code for the test sensor.

12. The sensor system of claim 10, wherein, If the measured temperature and the estimated temperature are both below the lowest temperature in the room temperature range and the absolute value of the difference between the measured temperature and the estimated temperature is greater than the limit residual threshold, then the controller is capable of operating to report a third error code for the test sensor.

13. A method for determining the suitability of temperature measurement by a thermistor temperature sensor in an analyte instrument, the analyte instrument including a biosensor interface and a controller, the biosensor interface being operable to connect to a test sensor containing a fluid sample, the method comprising: When connected to the test sensor having the fluid sample, an input signal is generated to the interface; Determine the output signal from the test sensor; Determine the measured temperature from the thermistor-based temperature sensor; The estimated temperature is determined by the temperature estimation algorithm through the controller. The controller determines the absolute value of the difference between the estimated temperature and the measured temperature. The controller selects one of the estimated temperature and the measured temperature based on the estimated temperature, the measured temperature, and the absolute value of the difference between the estimated temperature and the measured temperature. The selected estimated temperature or the measured temperature is provided as the temperature input for the analyte concentration determination algorithm; The analyte concentration is determined by executing the analyte concentration determination algorithm. as well as If the absolute value of the difference between the estimated temperature and the measured temperature is greater than the maximum allowable temperature compensation value, then an error code for the test sensor is reported.

14. The method of claim 13, wherein, The analyte is glucose and the fluid sample is blood.

15. The method of claim 13, wherein, The input signal is a gate control current analysis pulse.

16. The method of claim 13, wherein, The temperature estimation algorithm includes input variables determined by multiple regression analysis.

17. The method of claim 13, wherein, If the estimated temperature and the measured temperature are within the room temperature range, then the measured temperature is selected.

18. The method according to claim 17, wherein, The room temperature range includes high temperatures between 25°C and 30°C and low temperatures between 13°C and 20°C.

19. The method according to claim 13, wherein, If the measured temperature is outside the room temperature range, but the estimated temperature is less than the adjusted high temperature of the room temperature range and greater than the adjusted low temperature of the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the equilibrium threshold, then the estimated temperature is selected.

20. The method according to claim 19, wherein, The room temperature range includes a high temperature between 25°C and 30°C and a low temperature between 13°C and 20°C, wherein the adjusted high temperature is between 27°C and 34°C, the adjusted low temperature is between 11°C and 18°C, and the equilibrium threshold is between 3°C and 10°C.

21. The method of claim 13, further comprising: If the measured temperature and the estimated temperature are outside the room temperature range in opposite directions, a second error code for the test sensor is reported.

22. The method of claim 13, further comprising: If the measured temperature is within the room temperature range and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the residual limit threshold, then a second error code for the test sensor is reported.

23. The method of claim 22, further comprising: If the measured temperature and the estimated temperature are both higher than the highest temperature in the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the limit residual threshold, then the third error code of the test sensor is reported.

24. The method of claim 22, further comprising: If the measured temperature and the estimated temperature are both below the lowest temperature in the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the limit residual threshold, then a third error code for the test sensor is reported.

25. An analyte concentration sensor system for measuring analytes in a user's fluid sample, the sensor system comprising: A biosensor interface operable to connect to a test sensor that contains a fluid sample; A temperature sensor based on a thermistor, the temperature sensor being configured to measure temperature; A controller, coupled to the biosensor interface and the temperature sensor, is operable to: Generate an input signal that is fed into the biosensor interface; Read the output signal from the biosensor interface; Determine the measured temperature from the temperature sensor; Execute a temperature estimation algorithm to determine the estimated temperature; Determine the absolute value of the difference between the estimated temperature and the measured temperature; The fault of the test sensor is determined based on the estimated temperature, the measured temperature, and the absolute value of the difference between the estimated temperature and the measured temperature; The estimated temperature or the measured temperature is provided as the temperature input for the analyte concentration determination algorithm; The analyte concentration is determined by executing the analyte concentration determination algorithm. as well as If the absolute value of the difference between the estimated temperature and the measured temperature is greater than the maximum allowable temperature compensation value, then an error code for the test sensor is reported.

26. The sensor system of claim 25, wherein, The controller is further operable to select one of the estimated temperature and the measured temperature based on the estimated temperature, the measured temperature, and the absolute value of the difference between the estimated temperature and the measured temperature.

27. The sensor system of claim 25, wherein, The analyte is glucose and the fluid sample is blood.

28. The sensor system according to claim 25, wherein, The input signal is a gate control current analysis pulse.

29. The sensor system of claim 25, wherein, The temperature estimation algorithm includes input variables determined by multiple regression analysis.

30. The sensor system of claim 25, wherein, If the absolute value of the difference between the estimated temperature and the measured temperature is greater than the maximum allowable temperature compensation value, then the fault is determined.

31. The sensor system of claim 25, wherein, If the measured temperature and the estimated temperature are outside the room temperature range in opposite directions, then the fault is determined.

32. The sensor system of claim 25, wherein, If the measured temperature is within the room temperature range and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the residual limit threshold, then the fault is determined.

33. The sensor system of claim 32, wherein, If the measured temperature and the estimated temperature are both higher than the highest temperature in the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the limit residual threshold, then the fault is determined.

34. The sensor system according to claim 32, wherein, If the measured temperature and the estimated temperature are both lower than the lowest temperature in the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the limit residual threshold, then the fault is determined.

35. A method for determining a fault in a test sensor connected to an analyte instrument, the analyte instrument including a biosensor interface and a controller, the biosensor interface being operable to connect to the test sensor containing a fluid sample, the method comprising: When connected to the test sensor having the fluid sample, an input signal is generated to the interface; Determine the output signal from the test sensor; Determine the measured temperature from the thermistor-based temperature sensor; The controller uses a temperature estimation algorithm to determine the estimated temperature. The controller determines the absolute value of the difference between the estimated temperature and the measured temperature. The fault of the test sensor is determined based on the estimated temperature, the measured temperature, and the absolute value of the difference between the estimated temperature and the measured temperature; as well as The estimated temperature or the measured temperature is provided as the temperature input for the analyte concentration determination algorithm; The analyte concentration is determined by executing the analyte concentration determination algorithm. If the absolute value of the difference between the estimated temperature and the measured temperature is greater than the maximum allowable temperature compensation value, then an error code for the test sensor is reported.

36. The method of claim 35, further comprising: Based on the estimated temperature, the measured temperature, and the absolute value of the difference between the estimated temperature and the measured temperature, one of the estimated temperature and the measured temperature is selected.

37. The method of claim 35, wherein, The analyte is glucose and the fluid sample is blood.

38. The method of claim 35, wherein, The input signal is a gate control current analysis pulse.

39. The method of claim 35, wherein, The temperature estimation algorithm includes input variables determined by multiple regression analysis.

40. The method of claim 35, wherein, If the absolute value of the difference between the estimated temperature and the measured temperature is greater than the maximum allowable temperature compensation value, then the fault is determined.

41. The method of claim 35, wherein, If the measured temperature and the estimated temperature are outside the room temperature range in opposite directions, then the fault is determined.

42. The method of claim 35, wherein, If the measured temperature is within the room temperature range and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the residual limit threshold, then the fault is determined.

43. The method of claim 42, wherein, If the measured temperature and the estimated temperature are both higher than the highest temperature in the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the limit residual threshold, then the fault is determined.

44. The method according to claim 42, wherein, If the measured temperature and the estimated temperature are both lower than the lowest temperature in the room temperature range, and the absolute value of the difference between the estimated temperature and the measured temperature is greater than the limit residual threshold, then the fault is determined.

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