Tracking insertion and removal times of continuous glucose monitoring sensor

Abstract

To provide a tracking method and the like for an insertion time and a removal time of a continuous glucose monitoring sensor.SOLUTION: In response to insertion of a continuous glucose monitoring (CGM) sensor into the skin of a user, a CGM system compares an identifier of the sensor with any previously-stored identifiers of previously-inserted sensors. When the identifier does not match the previously-stored identifier, a newly-inserted sensor is indicated, the identifier and a time stamp are stored, and CGM may begin. Upon removal of the sensor, a removal time stamp is stored. When the identifier of an inserted sensor matches the previously-stored identifier, a reinserted sensor is indicated, a reinsertion time is obtained, and an elapsed removal time is checked to determine whether it exceeds a maximum removal time limit. In the case of affirmative determination, the CGM is halted. In the case of negative determination, the CGM may continue with the reinserted sensor.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This case claims the benefit of U.S. Provisional Patent Application No. 63 / 051,853, filed July 14, 2020, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

[0002] The present invention relates generally to continuous glucose monitoring (CGM). [Background technology]

[0003] CGM has become a routine monitoring operation in diabetes care. By providing real-time glucose readings, therapeutic actions can be applied in a more timely manner and glycemic conditions can be better controlled. During CGM operation, the sensor of the CGM device is typically inserted subcutaneously and operates continuously in an environment surrounded by tissue and interstitial fluid. The sensor inserted under the user's skin provides a signal to the wireless transmitter unit of the CGM device that is indicative of the user's glucose level. Glucose readings can be performed automatically multiple times throughout the day (e.g., every few minutes or at some other pre-established time interval).

[0004] The CGM device may be attached to the exterior surface of the user's skin, such as the abdomen or the back of the upper arm, while the sensor is inserted through the skin and contacts the interstitial fluid. The sensor interacts with the interstitial fluid and generates electrical signals proportional to the amount of glucose present. These electrical signals are communicated to a transmitter unit for use in determining glucose levels.

[0005] CGM devices can be worn on the body for days or weeks before the sensor needs to be removed and replaced. In some cases, the sensor may need to be removed and reinserted, for example, to address issues with the CGM device's adhesion to the user's skin. Summary of the Invention

[0006] In some embodiments, a continuous glucose monitoring (CGM) system is provided that includes a sensor unit having a sensor unit memory and a sensor, the sensor unit memory having an identifier stored therein. The CGM system also includes a second memory configured to store a plurality of sensor identifiers therein. The CGM system further includes a real-time clock and a processor in communication with the second memory, the real-time clock, and the sensor unit. The processor is configured to execute computer instructions to: (1) read the identifier stored in the sensor unit memory; (2) determine whether the identifier matches any previously stored identifiers in the second memory; (3) store the identifier and an insertion timestamp in the second memory in response to the identifier not matching any previously stored identifiers in the second memory, the real-time clock being used to generate the insertion timestamp; (4) obtain a reinsertion time using the real-time clock in response to the identifier matching the identifier previously stored in the second memory; and (5) use the reinsertion time to determine whether the sensor has exceeded a predetermined maximum removal time limit.

[0007] In some embodiments, a continuous glucose monitoring (CGM) system is provided that includes a sensor configured to be inserted into a user's skin and generate an electrical signal indicative of a glucose level. The CGM system also includes a real-time clock, a first memory having stored therein an identifier that identifies the sensor, a second memory configured to store therein a plurality of sensor identifiers, and a processor in communication with the real-time clock and the first and second memories. The processor is configured to execute computer instructions to: (1) read the identifier stored in the first memory; (2) determine whether the identifier matches any previously stored identifiers in the second memory; (3) store the identifier and an insertion timestamp in the second memory in response to the identifier not matching any previously stored identifiers in the second memory, the real-time clock being used to generate the insertion timestamp; (4) obtain a reinsertion time using the real-time clock in response to the identifier matching the identifier previously stored in the second memory; and (5) determine whether the sensor has exceeded a predetermined maximum removal time limit using the reinsertion time.

[0008] In some embodiments, a method for tracking insertion and removal times of a continuous glucose monitoring (CGM) sensor is provided, the method including: in response to activation of the CGM, reading an identifier of the sensor from a sensor unit memory via a processor executing computer instructions, determining whether the identifier matches any previously stored identifiers in a second memory, storing the identifier and the insertion timestamp in the second memory in response to the identifier and the insertion timestamp not matching any previously stored identifiers in the second memory, obtaining a reinsertion time in response to the identifier matching the previously stored identifier in the second memory, using the reinsertion time to determine whether the sensor has exceeded a predetermined maximum removal time limit, and ceasing operation of the CGM in response to determining that the sensor has exceeded the predetermined maximum removal time limit.

[0009] Further aspects, features, and advantages of the present disclosure will become readily apparent from the following detailed description and illustrations of several exemplary embodiments and implementations, including the best mode contemplated for carrying out the invention. The present disclosure may enable other different embodiments, and its several details may be modified in various respects, without departing from the scope of the present invention. For example, although the following description relates to continuous glucose monitoring, the devices, systems, and methods described below may be readily adapted to monitoring other analytes, such as cholesterol, lactate, uric acid, alcohol, and the like, in other continuous analyte monitoring systems. The present disclosure is intended to cover all modifications, equivalents, and alternatives within the scope of the appended claims (see further below). [Brief explanation of the drawings]

[0010] The drawings described below are for illustrative purposes and are not necessarily drawn to scale. Accordingly, the drawings and descriptions should be regarded as illustrative in nature, and not as restrictive. The drawings are not intended to limit the scope of the invention in any way. [Figure 1] 1 illustrates a side view of a continuous glucose monitoring (CGM) device including a sensor unit and a transmitter unit according to embodiments provided herein. [Figure 2] 2 illustrates a block diagram of the CGM device of FIG. 1 according to embodiments provided herein. [Figure 3] 1 illustrates a block diagram of a CGM system including a CGM device and an external device, according to embodiments provided herein. [Figure 4] 1 illustrates a flowchart of a method for tracking insertion and removal times of a CGM sensor, according to embodiments provided herein. [Figure 5A]10 illustrates a table stored in memory listing CGM sensor identifiers, various timestamps, maximum insertion time limits, and elapsed insertion times, each according to an embodiment provided herein. [Figure 5B] 10 illustrates a table stored in memory listing CGM sensor identifiers, various timestamps, maximum insertion time limits, and elapsed insertion times, each according to an embodiment provided herein. [Figure 5C] 10 illustrates a table stored in memory listing CGM sensor identifiers, various timestamps, maximum insertion time limits, and elapsed insertion times, each according to an embodiment provided herein. [Figure 5D] 10 illustrates a table stored in memory listing CGM sensor identifiers, various timestamps, maximum insertion time limits, and elapsed insertion times, each according to an embodiment provided herein. DETAILED DESCRIPTION OF THE INVENTION

[0011] To more closely monitor and detect changes in a person's glucose concentration level, continuous glucose monitoring (CGM) methods and systems have been developed. CGM methods and systems typically generate electrochemical glucose signals continuously during operation and perform glucose measurements / estimations based on the generated signals, typically every few minutes.

[0012] CGM systems generally have a wearable portion (CGM device) that is worn on the body and communicates (e.g., wirelessly) with an external device, such as a handheld CGM receiver or other portable device like a smartphone running a suitable application software program. The CGM device may be worn for several days or for one or two weeks before needing to be removed and replaced. The CGM device includes a sensor that is inserted subcutaneously (implanted). The CGM device may also include analog circuitry coupled to the sensor and configured to bias the sensor and measure a current signal generated by the inserted sensor in contact with interstitial fluid. The CGM device may also include processing circuitry for determining a glucose concentration level based on the measured current signal. The CGM device may further include electronic transmitter circuitry for communicating the determined glucose level to an external device (e.g., a smart device or CGM receiver). The CGM device may be attached to an external surface of the skin, such as the abdomen, the back of the upper arm, or another suitable location, for example, via adhesive.

[0013] CGM systems may provide frequent measurements of a user's glucose level without the need for each such measurement to involve drawing a blood sample, such as a finger stick. CGM systems may still occasionally use a finger stick and the use of a blood glucose monitoring (BGM) system, such as the Contour NEXT One® by Ascensia Diabetes Care AG of Basel, Switzerland, to initiate calibration of the CGM system.

[0014] The CGM device of a CGM system may typically be worn for up to about two weeks, after which the sensor may be removed and replaced. In some embodiments, the entire CGM device may be removed and replaced. In another embodiment, the CGM device may include a replaceable sensor unit that can be detached by the user from the reusable transmitter unit of the CGM device. In such an embodiment, only the sensor unit of the CGM device may need to be removed and replaced.

[0015] A CGM system may be configured to notify a user, for example, via a display message and / or an audible alert, when a sensor has reached its maximum allowable insertion time limit (e.g., 10 or 14 days) and should be replaced. The CGM system may also prevent glucose measurements from occurring with such an EOL (“end-of-life”) sensor. However, a user may attempt to reuse an EOL sensor by removing the sensor from the user's skin surface and then reinserting it into the skin as if it were new. For numerous health and performance reasons, a CGM system configured to prevent this from happening would be desirable. However, a user may also experience problems with a CGM device during operation, such as problems with the CGM device adhering to the user's skin surface, requiring the user to remove and reinsert the sensor to correct the problem. The CGM system would also desirably be configured to distinguish this situation from an attempt to reuse an EOL sensor. It would further be desirable for the CGM system to determine and prevent a reinserted sensor from being used if it has been removed from the user's skin surface for too long. Such sensors are no longer sterile and may be contaminated, which may lead to health and / or other problems if reused.

[0016] According to one or more embodiments, provided herein are devices, systems, and methods for tracking CGM sensor insertion and removal times and subsequent detection of exceeding a maximum removal time limit and / or a maximum insertion time limit, as described in more detail below in connection with FIGS. 1-5D.

[0017] FIG. 1 illustrates a wearable CGM device 100 inserted into a user's skin 102, according to one or more embodiments. The CGM device 100 is configured to continuously monitor and provide glucose measurements periodically (e.g., every 5 minutes or other suitable time intervals). While the CGM device 100 is shown as partially dome-shaped, the CGM device 100 may have other shapes. The CGM device 100 may include a sensor unit 104 and a transmitter unit 106. In some embodiments, the sensor unit 104 and the transmitter unit 106 may be integrally formed. In other embodiments, the sensor unit 104 may be disposable and detachable from the transmitter unit 106, which may be replaceable and reusable with other sensor units. The sensor unit 104 and the transmitter unit 106 may be physically connected together via any suitable mechanical mechanism. The sensor unit 104 and the transmitter unit 106 may also be electrically coupled together such that, when physically connected, data and control signals may be communicated and transmitted between electrical components within the sensor unit 104 and the transmitter unit 106. In some embodiments, initiation of communication between the sensor unit 104 and the transmitter unit 106 may be in response to physically connecting the two units together. In other embodiments, communication may be initiated by a command, such as a start command. Communication between the sensor unit 104 and the transmitter unit 106 may be initiated in other suitable ways.

[0018] The sensor unit 104 may include a sensor 108, a portion of which is shown to be inserted through the user's skin 102. The sensor 108 may extend from the sensor unit 104 through a base plate 110 and may be configured to reside at least partially within interstitial fluid in the user's subcutaneous region. The sensor 108 may be or include an analyte sensor or analyte sensor portion, such as at or near a sensor tip 108T. The sensor 108 may be inserted with an insertion device (not shown) having a sharp needle or "introducer" that pierces the skin to introduce the sensor 108 into the user's subcutaneous region. Any suitable insertion device may be used.

[0019] The sensor unit 104 may also include an adhesive layer 112, which may be, for example, double-sided tape or a pressure-sensitive adhesive. One side of the adhesive layer 112 may adhere to the base plate 110, while the other side of the adhesive layer 112 may adhere to the user's skin surface 102S.

[0020] The transmitter unit 106 may include one or more electronic components that communicate with one or more electronic components within the sensor unit 104 and with one or more external devices, as described in more detail below.

[0021] 2 illustrates a circuit component configuration 200 of a CGM device 100 according to one or more embodiments. The sensor unit 104 may include a sensor assembly 214 and a sensor unit memory 216. The sensor assembly 214 may include a sensor 108 and a sensor circuit (not shown separately) coupled to the sensor 108. The sensor circuit may apply at least one bias voltage to an analyte sensor portion of the sensor 108, which may generate an electrical signal while the sensor 108 is in contact with interstitial fluid. The sensor circuit may also facilitate conduction of the electrical signal between the sensor tip 108T of the sensor 108 and / or other portions of the sensor 108.

[0022] The sensor unit memory 216 may include programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), write-once-read-many memory (WORM), static random access memory (SRAM), synchronous dynamic random access memory (SDRAM), physically unclonable function (PUF) (which may serve as a unique identifier), and / or NOR and NAND flash memory. Other suitable types of sensor memory circuits may be used for the sensor unit memory 216.

[0023] In some embodiments, the sensor unit memory 216 may include radiation-resistant memory (rad-hard memory) or may be located in rad-hard packaging that retains information (e.g., data) stored therein when the packaging and / or memory is exposed to radiation used to sterilize the sensor unit 104.

[0024] The sensor unit memory 216 may store sensor information specific to its individual sensor unit and internal components. For example, the sensor information may include a sensor unit identifier (e.g., the sensor unit's serial number), a corresponding maximum insertion time limit (e.g., 3, 10, or 14 days), and a corresponding maximum removal time limit (e.g., 15, 45, or 60 minutes). The identifier may be unique or at least partially unique (e.g., a manufacturer may not reuse the same identifier for a particular period of time or within a particular geographic area, so that a user is unlikely to insert a sensor with the same identifier as a different, recently inserted sensor). The maximum insertion time limit is the period after which the sensor should be removed and replaced (i.e., the sensor has reached EOL). The maximum removal time limit is the period after which a sensor removed from a user's skin is considered unsuitable for reinsertion (e.g., for health or performance reasons) and therefore should not be reinserted even if the maximum insertion time limit has not been reached.

[0025] In some embodiments, the sensor information may also include, for example, one or more of the following parameters: a) electrode sensitivity gradient; b) date of manufacture; c) expiration date (storage period), d) batch or lot number; e) Security code, and / or f) Memory device version.

[0026] Other parameters and / or sensor information may be stored in sensor unit memory 216. Additionally or alternatively, some or all of the above parameters and / or sensor information may be encoded, such as in a barcode attached to sensor unit 104, CGM device 100, and / or its packaging.

[0027] In some embodiments, electrical data and control signals and power may be transmitted between the sensor unit 104 and the transmitter unit 106 via the connector 218, electrical contact pads 220 and 222 on the sensor unit 104, and electrical contact pads 224 and 226 on the transmitter unit 106 when the sensor unit 104 and the transmitter unit 106 are physically connected together.

[0028] The transmitter unit 106 may include an analog front end 228, a microcontroller 230 (or other similar processing resources), memory 232, a real-time clock 233, a wireless transmitter 234, a switch 235, and a power source such as a battery 236. In some embodiments, the transmitter unit 106 may include a local display (not shown) for displaying information such as glucose concentration information, sensor EOL, etc. without the use of an external device.

[0029] The analog front end 228 may be configured to drive the sensor assembly 214 and / or process sensor data generated by the sensor assembly 214 and the sensor 108. For example, the analog front end 228 may be configured to apply a bias voltage to the sensor assembly 214 and measure the resulting current through the sensor assembly 214. The analog front end 228 in conjunction with the sensor assembly 214 may apply a bias voltage to an inserted sensor 108 located in the interstitial fluid and measure the resulting current proportional to the glucose concentration. The analog front end 228 may perform other, fewer, or more functions.

[0030] Microcontroller 230 may be coupled to analog front end 228, memory 232, real-time clock 233, wireless transmitter 234, switch 235, and battery 236, and possibly other circuitry (not shown). Microcontroller 230 may include a processor, such as, for example, a microprocessor or other suitable processing circuitry, to process sensor data generated by sensor assembly 214 and / or analog front end 228 and to detect sensor reinsertion as described herein. Microcontroller 230 may also include, for example, an analog-to-digital converter for converting the analog current signal generated by sensor assembly 214 to a digital current signal. Microcontroller 230 may further store the digital current signal value in memory 232 and / or calculate or estimate a glucose concentration level based at least in part on the digital current signal. Microcontroller 230 may also further detect whether a sensor of the CGM device has met its maximum insertion time limit and / or whether a sensor of the CGM device has been reinserted and whether the reinserted sensor has exceeded its maximum removal time limit, as described in more detail below in connection with FIGS. 4-5D . Microcontroller 230 may perform other suitable functions.

[0031] The microcontroller 230 and / or other circuitry within the transmitter unit 106 may be electrically coupled to and configured to communicate with the sensor unit memory 216. The microcontroller 230 may receive data stored in the sensor unit memory 216, including, for example, an identifier for the sensor unit 104 and maximum insertion and removal time limits, along with other of the sensor information described above related to one or more parameters of one or more components of the sensor unit 104. In some embodiments, a signal (e.g., a pull signal) may be sent from the microcontroller 230 to the sensor unit memory 216 to cause the sensor unit memory 216 to transmit data without user input. Thus, the sensor unit memory 216 may automatically transmit data to the microcontroller 230 in response to connecting the sensor unit 104 to the transmitter unit 106. Alternatively, transmission of sensor information from the sensor unit memory 216 to the microcontroller 230 may occur by a prompt, such as from an external device, or in any other suitable manner.

[0032] Microcontroller 230 may store information received from sensor unit memory 216 in memory 232 and may use the information when calculating analyte concentrations, when detecting whether sensor 108 has been reinserted (and, if so, whether sensor 108 has met and / or exceeded maximum insertion and removal time limits), and when performing other functions. In other embodiments, the information may remain in sensor unit memory 216 and may be accessed as needed during CGM processing by microcontroller 230 or other circuitry.

[0033] Additionally or alternatively, the microcontroller 230 and memory 232 may receive sensor information from the sensor unit 104, one or more barcodes attached to the CGM device 100 and / or its packaging, or the like, via scanning by an external device in communication with the transmitter unit 106.

[0034] The memory 232 may include computer program code stored therein that, when executed by a processor within the microcontroller 230, causes the CGM device 100 to perform various functions and / or communicate with one or more external devices, such as a CGM receiver or smart device (e.g., a smartphone or tablet) running a CGM application software program that may calculate and / or display glucose levels and related data.

[0035] The memory 232 may also be configured to store multiple sensor unit identifiers corresponding to previously used sensor units in embodiments where the sensor unit 104 is replaceable and detachable from the transmitter unit 106 for reuse with other sensor units. In some embodiments, the identifiers corresponding to previously used sensor units may be stored, for example, in cloud-based storage and downloaded to the memory 232 as needed.

[0036] The memory 232 may further include computer program instructions stored therein that, when executed by the processor within the microcontroller 230, cause the CGM device 100 to, in part, determine whether the identifier stored in the sensor unit memory 216 matches any previously stored identifiers within the memory 232, and, in response to determining that the identifier stored in the sensor unit memory 216 matches any previously stored identifiers within the memory 232, determine whether the sensor 108 has exceeded a predetermined maximum removal time limit.

[0037] In some embodiments, memory 232 may be radiation-hard memory (rad-hard memory) or may be located in a rad-hard package similar to or the same as sensor unit memory 216. Memory 232 may be non-volatile memory and may include, but is not limited to, electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and / or flash memory (e.g., a type of EEPROM in either a NOR or NAND configuration). Other types of suitable memory may be used for memory 232, including reading data from an internet storage location, which may be cloud-based.

[0038] In some embodiments, the switch 235 may be any suitable mechanical or electrical switch that indicates whether the sensor unit 104 is physically and electrically connected to the transmitter unit 106. That is, the switch 235 may have one output that indicates that the sensor unit 104 is physically and electrically connected to the transmitter unit 106 and another output that indicates that the sensor unit 104 is not physically and electrically connected to the transmitter unit 106 (e.g., when the sensor 108 is removed from the user's skin).

[0039] In addition to or alternatively to switch 235, in other embodiments, the computer program instructions stored in memory 232 or the CGM application software program executing on the external device may have an encoded "software switch" that monitors whether any current is received from sensor 108. If no current is received (or measured), the software switch may indicate an error condition (e.g., that sensor 108 has been removed from the user's skin).

[0040] The battery 236 may be located in the transmitter unit 106 and may provide power to the transmitter unit 106. In some embodiments, the battery 236 may be rechargeable. When the sensor unit 104 is connected to the transmitter unit 106, the battery 236 may also provide power to the sensor unit 104. Providing power to the sensor unit 104 may, in some embodiments, initiate communication between the sensor unit 104 and the transmitter unit 106, initiate sensor insertion detection, and / or initiate CGM processing. In some embodiments, power may be provided to the sensor unit 104 via the analog front end 228. In other embodiments, the battery 236 may be located in the sensor unit 104 instead of the transmitter unit 106, and in still other embodiments, the sensor unit 104 and the transmitter unit 106 may each have their own battery. Examples of the battery 236 include coin-cell batteries such as flexible lithium polymer batteries, lithium manganese, silver oxide, and alkaline coin cells (e.g., CR2032, SR516, and LR60 type coin cells), etc. Other power supply / battery types may be used.

[0041] In some embodiments, microcontroller 230 may transmit electrical signals, glucose concentration information, and / or other information to one or more external devices via wireless transmitter 234. In some embodiments, microcontroller 230 may receive electrical signals, instructions, data, and / or other information from one or more external devices via wireless transmitter 234.

[0042] 3 illustrates a CGM system 300 according to one or more embodiments. The CGM system 300 includes a CGM device 100 and an external device 330. The external device 330 may be, for example, a dedicated CGM receiver or a smart device running a CGM application software program. The external device 330 may include a processor 331, memory 332, a real-time clock 333, a wireless transmitter 334, and a display 336, where the processor 331 is coupled to each of the memory 332, the real-time clock 333, the wireless transmitter 334, and the display 336, each of which may be any suitable device or component configured to perform at least some or all of the CGM-related functions described herein. The external device 330 may include other circuit components as well.

[0043] The external device 330 and the CGM device 100 may be communicatively coupled to one another via their respective wireless transmitters 234 and 334. Such wireless communication may occur via any suitable standards-based communication protocol, such as, for example, the Bluetooth® communication protocol. In some embodiments, wireless communication between the external device 330 and the CGM device 100 may occur via near field communication (NFC), radio frequency (RF) communication, infrared (IR) communication, optical communication, or any other suitable type of wireless communication. In some embodiments, the external device 330 and the CGM device 100 may additionally or alternatively communicate via one or more wired connections. In some embodiments, a security code matching a security code stored in the sensor unit memory 216 may need to be entered by the user into the external device 330 before communication can begin between the sensor unit 106 and the sensor unit 104 and / or between the CGM device 100 and the external device 330.

[0044] In some embodiments, at least a portion of the sensor information stored in the sensor unit memory 216 of the sensor unit 104 may be transferred to the memory 332 of the external device 330 via the wireless transmitter 234 of the CGM device 100 and the wireless transmitter 334 of the external device 330. The received sensor information may be processed by the processor 331 and displayed on the display 336. In some embodiments, some or all of the processing for determining the glucose level may be performed by the processor 331 instead of the transmitter unit 106 and displayed on the display 336. Other sensor information received by the external device 330 may be displayed on the display 336 to the user of the CGM device 100. For example, the manufacturing date and / or expiration date of the sensor 108 and / or sensor unit 104 may be provided to the user, which may allow the user to determine whether to use the sensor unit 104 and / or CGM 100.

[0045] In some embodiments, some or all of the processing for detecting reinsertion of the sensor 108 and determining whether the reinserted sensor has exceeded its maximum removal time limit as described herein in connection with the transmitter unit 106 may be performed by the external device 330 rather than the transmitter unit 106. Specifically, for example, the memory 332 of the external device 330 may be configured to store multiple sensor unit identifiers corresponding to previously used CGM devices (in embodiments in which the sensor unit 104 and transmitter unit 106 are integrally formed) or previously used sensor units (in embodiments in which the sensor unit 104 is replaceable and detachable from the transmitter unit 106 and reusable with other sensor units). Also, in some embodiments, the sensor information / data may be stored in cloud-based storage and retrieved from there to the memory 332 by the external device 330 as needed. In other embodiments, some or all of the sensor information / data may be encoded, such as in one or more barcodes attached to the sensor unit 104, the CGM device 100, and / or their packaging, and retrieved therefrom to the memory 332 by a scanner (not shown) of the external device 330.

[0046] In embodiments in which the sensor unit 104 and transmitter unit 106 are integrally formed, requiring the CGM device 100 to be removed and replaced at the end of life of the sensor 108, an identifier (e.g., serial number) of the CGM 100 may be stored in either the sensor unit memory 216 or the memory 232 of the transmitter unit 106 and / or in its barcode. In some embodiments, a CGM device 100 with an integrally formed sensor unit 104 and transmitter unit 106 may have only a single memory in which the identifier may be stored (e.g., the sensor unit memory 216 and memory 232 may be combined into a single memory device, which may still be referred to as the sensor unit memory). The CGM identifier may be transferred to the memory 332 of the external device 330 in response to insertion or reinsertion of the CGM device 100 into the user's skin.

[0047] The memory 332 of the external device 330 may include computer program instructions, which may be part of an internally stored CGM application software program, that, when executed by the processor 331, cause the processor 331 to, in part, determine whether the identifier stored in the CGM device 100 matches any previously stored identifiers in the memory 332, and, in response to determining that the identifier stored in the CGM device 100 matches any previously stored identifiers in the memory 332, determine whether the sensor 108 has exceeded its predetermined maximum removal time limit.

[0048] 4 illustrates a method 400 for tracking the insertion and removal time of sensors in a CGM device. In some embodiments, the method 400 may also determine whether a reinserted sensor has exceeded a maximum removal time limit and should not be used. In yet other embodiments, the method 400 may determine whether a reinserted sensor has met its maximum insertion time limit and should be removed and replaced.

[0049] At processing block 402, method 400 may begin by reading or receiving an identifier of the inserted sensor via a processor executing computer instructions in response to activation of the CGM. Activation of the CGM may occur in response to powering on the sensor unit, in response to a command entered by the user, in response to insertion of the sensor into the user's skin, or in any other suitable manner of initiating CGM. The identifier may be stored, for example, in a sensor unit memory of the sensor unit and / or encoded, for example, in a bar code attached to the sensor unit, the CGM device, or their packaging. In some embodiments, the sensor may be sensor 108 of sensor unit 104 of CGM device 100, which may be part of CGM system 300 (see FIGS. 1-3). The sensor unit memory may be sensor unit memory 216, and the processor may be a processor of microcontroller 230 of CGM device 100, or processor 331 of an external device 330 in communication with CGM device 100.

[0050] The method 400 may proceed to decision block 404 to determine whether the sensor identifier matches any identifiers of previously inserted sensors stored in a second memory. The second memory may be, for example, memory 232 located within transmitter unit 106 of CGM device 100 or memory 332 of external device 330. In some embodiments, the second memory may include a table such as those shown in each of Figures 5A-5D.

[0051] 5A, 5B, 5C, and 5D illustrate stored tables 500A, 500B, 500C, and 500D, respectively, which each list a sensor identifier (“ID”) for a currently inserted sensor and / or a previously inserted sensor and a corresponding insertion timestamp, maximum allowable insertion time, elapsed insertion time, removal timestamp, and optional reinsertion timestamp. Each of the insertion, removal, and optional reinsertion timestamps may have a month:day:hour:minute format, for example, which may be provided by a real-time clock such as real-time clock 233 or 333 (of FIGS. 2 and 3, respectively). The maximum allowable insertion time and elapsed insertion time may have a day:hour:minute format, for example. Other suitable formats may be used for each entry. In some embodiments, an additional column for a maximum allowable removal time limit may also be included.

[0052] Returning to decision block 404 , if the determination is “no,” indicating that the sensor identifier is not in the second memory, the sensor is presumed to be new and method 400 may proceed to process block 406 .

[0053] In processing block 406, the second memory is updated to include the new identifier, the corresponding insertion timestamp, and the maximum allowable insertion time for the sensor (which may have been read or received, e.g., from the sensor unit memory or an attached barcode). The entries for the elapsed insertion time, removal timestamp, and optional reinsertion timestamp may each be zeroed. For example, with reference to FIG. 5A , assume a newly inserted sensor has an identifier 1234567, which does not match any previously stored identifiers. In response, the second memory is updated with the sensor identifier 1234567, the insertion timestamp 06:19:08:32 (in month:day:hour:minute format, indicating that the newly inserted sensor was inserted at 8:32 AM on June 19th), and the maximum insertion time 14:00:00 (in day:hour:minute format, indicating that the maximum allowable insertion time for this sensor is 14 days). As shown in FIG. 5A, the most recent previously inserted sensor had identifier 8765432, and the sensor before that had identifier 4321876.

[0054] The method 400 may then proceed to process block 408 where data from the sensor is read and the glucose level is determined / estimated based on the sensor data, as described above.

[0055] After each sensor reading and glucose level determination / estimation in process block 408 (which may occur at a predetermined measurement interval, such as every 5 minutes), method 400 may proceed to decision block 410 to determine whether to update the elapsed insertion time of the currently inserted sensor. The update may occur at any suitable time interval (e.g., every 5 minutes, every hour or more, once a day, etc.), which is preferably an even multiple of the maximum insertion time limit.

[0056] If the determination is "yes" at decision block 410, indicating that the elapsed insertion time of the sensor should be updated, method 400 may proceed to process box 412 where the elapsed insertion time of the currently inserted sensor may be updated in a table stored in the second memory. Referring to FIG. 5B, for example, currently inserted sensor 1234567 is shown in table 500B as having an updated elapsed insertion time of 5 days, 14 hours, and 30 minutes.

[0057] In an alternative embodiment, instead of periodically updating the elapsed insertion time entry in the table stored in the second memory, processing block 412 may periodically increment an elapsed insertion time counter while the sensor is inserted.

[0058] If the determination is "no" at decision block 410, indicating that the elapsed insertion time of the sensor does not need to be updated, method 400 may proceed to decision block 411, where continued insertion of the sensor is checked. That is, method 400 checks whether the sensor has been removed from the user's skin. Sensor removal may be detected, for example, via switch 235 (see FIG. 2 ) of transmitter unit 106, which indicates whether sensor unit 104 is connected to transmitter unit 106. Disconnection may indicate that sensor unit 104 (and sensor 108) has been removed from the user's skin. Sensor removal may alternatively or additionally be detected via software when electrical signals from sensor 108 are no longer received by transmitter unit 106, which may indicate that sensor 108 is no longer in contact with the user's interstitial fluid.

[0059] If the determination is "No" at decision block 411, indicating that the sensor has not been removed, method 400 returns to process block 408 to continue glucose monitoring. (A "Yes" determination at decision block 411 is described further below.)

[0060] From process block 412, method 400 may proceed to decision block 414 to determine whether the sensor has met its maximum insertion time limit. A “yes” determination at decision block 414 indicates that the sensor's elapsed insertion time, as indicated by either the table stored in the second memory or the elapsed insertion time counter, is equal to the sensor's maximum insertion time limit. Note that in embodiments where the update interval is not an even multiple of the maximum insertion time limit, the elapsed insertion time may exceed the sensor's maximum insertion time limit. An elapsed insertion time equal to (or exceeding) the maximum insertion time limit at decision block 414 indicates that the sensor has reached its EOL and should no longer be used. For example, with reference to any of FIGS. 5A-5D , assume sensor 4321876 is the currently inserted sensor. As shown, sensor 4321876 has a maximum insertion time of 14 days and an elapsed time of 14 days. Thus, method 400 determines that sensor 4321876's maximum insertion time has been met and the sensor should no longer be used. The method 400 may then proceed to process block 416 .

[0061] At processing block 416, operation of the sensor is stopped. That is, the processor of the CGM device 100 and / or external device 330 may signal the user with an error message or an audible alert via an I / O device (e.g., a display and / or sound device) of the CGM device 100 and / or external device 330 that glucose monitoring has ceased and the sensor needs to be replaced. In some embodiments, the CGM device 100 and / or external device 330 may prevent the sensor from operating and / or may prevent processing of any signals received from the sensor. Method 400 may end here until a sensor (either new or previously used) is inserted into the user's skin, which returns method 400 to processing block 402.

[0062] Returning to decision block 414, a "no" determination indicates that the sensor has not met its maximum insertion time and is therefore still usable. For example, with reference to FIG. 5B, method 400 determines whether sensor 1234567's elapsed insertion time of 5 days, 14 hours, and 30 minutes equals (or exceeds) sensor 1234567's maximum insertion time limit of 14 days. Because it is not, method 400 may proceed to decision block 411, where continued insertion of the sensor is checked, as described above and below.

[0063] If the determination is 'yes' at decision block 411 , indicating that the sensor has been removed, the method 400 may proceed to process block 413 .

[0064] At process block 413, method 400 may store in a second memory a removal timestamp corresponding to the just-removed sensor. For example, with reference to FIG. 5C, assume method 400 detects the removal of sensor 1234567 at 5:47 PM on June 26. Thus, a removal timestamp of 06:26:17:47 may be stored in table 500C corresponding to sensor 1234567.

[0065] Next, method 400 may proceed to process block 415, where the elapsed insertion time corresponding to the removed sensor is updated based on the removal timestamp. For example, referring again to FIG. 5C, the elapsed insertion time for sensor 1234567 is updated to 07:09:15 (7 days, 9 hours, 15 minutes) based on the time difference between the removal timestamp (06:26:17:47) and the insertion timestamp (06:19:08:32).

[0066] In an alternative embodiment in which an elapsed insertion time counter is used as described above in connection with processing block 412, method 400 at processing block 415 may instead store the value of the elapsed insertion time counter in a second memory in response to detecting at decision block 411 that the sensor has been removed.

[0067] Method 400 may end at process block 415 until a sensor (new or previously used) is inserted into the user's skin, at which point method 400 begins again at process block 402 .

[0068] When method 400 returns to decision block 404, where it determines whether the identifier of the sensor being inserted into the user's skin matches any identifiers of previously inserted sensors stored in the second memory, a "yes" determination indicates that the sensor identifier matches an identifier previously stored in the second memory, and therefore the sensor is presumed to have been reinserted and reused. Method 400 may then proceed to processing block 405.

[0069] In processing block 405, method 400 may obtain a reinsertion time from a real-time clock, such as one of real-time clocks 233 or 333, and may optionally store a reinsertion timestamp corresponding to the reinserted sensor in a second memory. For example, with reference to FIG. 5D , assume sensor 1234567 was removed (e.g., to adjust or replace an adhesive used to attach the sensor unit or CGM device to the user's skin surface) and has now been reinserted. For example, a reinsertion timestamp of 06:26:18:04 indicates that the sensor was reinserted at 6:04 PM on June 26th, and may optionally be stored in table 500D corresponding to sensor 1234567.

[0070] Method 400 may now proceed to decision block 407 to determine whether the sensor's maximum removal time limit has been exceeded. The maximum removal time limit may be stored in memory in the sensor unit, transmitter unit, or cloud service, or may be encoded in a barcode, CGM application software program, or firmware on the CGM device. The maximum removal time limit may be established in accordance with safe medical practices for subcutaneous implantation and may range, for example, from several minutes to approximately one hour. Other maximum removal time limits may be possible. In some embodiments, tables 500A-500D may include additional columns for storing maximum removal time limits. To determine whether the sensor's maximum removal time limit has been exceeded, method 400 determines the elapsed removal time by calculating the time difference between the reinsertion time (obtained directly from the real-time clock or the reinsertion timestamp) and the removal timestamp. For example, referring to FIG. 5D, the time difference between the reinsertion timestamp of sensor 1234567 and the removal timestamp of sensor 1234567 is 17 minutes (06:26:18:04 to 06:26:17:47).

[0071] If the determination is "no" at decision block 407, indicating that the sensor has not exceeded its maximum removal time limit and therefore may be suitable for continued use, method 400 may proceed to decision block 414 to determine whether this previously inserted sensor meets its maximum insertion time limit as described above. This may prevent the EOL sensor from being reused.

[0072] Note that a reinserted sensor that does not meet the maximum insertion time limit determined in decision block 414 may continue to be used. In some embodiments, further updating of the elapsed insertion time in process block 412 may continue based on the insertion timestamp, or may be based on the optional insertion timestamp in embodiments where one is stored.

[0073] If the determination is "yes" at decision block 407, indicating that the sensor has exceeded its maximum removal time limit and therefore should not be used, method 400 may proceed to processing block 416 where any continued use of this sensor is prevented, as described above.

[0074] In alternative embodiments, tables 500A-500D may each include an error detection column to indicate any error, defect, fault, or failure of the sensor, replaceable sensor unit, or replaceable CGM device detected during power-on or use that would prohibit continued use of the sensor, replaceable sensor unit, or replaceable CGM device even though the sensor's maximum insertion time limit has not yet been met. In these alternative embodiments, alternative decision block 414 may also determine whether any such error, defect, fault, or failure has occurred (as indicated in its error detection column) in addition to determining whether the sensor's maximum insertion time limit has been met. In response to a determination that such an error, defect, fault, or failure has occurred or that the sensor's maximum insertion time limit has been met, alternative method 400 would proceed to block 416 to stop operation of the sensor. In response to a determination that an error, defect, fault, or failure has occurred and the sensor's maximum insertion time limit has not been met, alternative method 400 would proceed as described above.

[0075] Note that in some embodiments, tables 500A-500D may store only a small number of identifiers (e.g., 5-10) corresponding to recently used sensors. In some embodiments, tables 500A-500D may be stored in memory 232 of transmitter unit 106, while in other embodiments, tables 500A-500D may be stored in memory 332 of external device 330 or in cloud-based memory.

[0076] It is also noted that some embodiments, or portions thereof, may be provided as a computer program product or software, which may include a machine-readable medium having stored thereon non-transitory instructions that may be used to program a computer processor, system, controller, or other electronic device to perform the processes or methods described herein in accordance with one or more embodiments.

[0077] While the present disclosure is susceptible to various modifications and alternative forms, specific method and apparatus embodiments have been shown by way of example in the drawings and are herein described in detail. It will be understood, however, that the specific methods and apparatus disclosed herein are not intended to limit the scope of the disclosure or the claims.

Claims

1. 1. A continuous glucose monitoring (CGM) system comprising: a sensor unit having a sensor unit memory and a sensor, the sensor unit memory having an identifier stored therein; a second memory configured to store therein a plurality of sensor identifiers; A real-time clock and a processor in communication with the second memory, the real-time clock, and the sensor unit, the processor comprising: reading the identifier stored in the sensor unit memory; determining whether the identifier matches any previously stored identifier in the second memory; responsive to the identifier not matching any previously stored identifier in the second memory, storing the identifier and an insertion timestamp in the second memory, wherein the real time clock is used to generate the insertion timestamp; responsive to the identifier matching an identifier previously stored in the second memory, obtaining a reinsertion time using the real time clock; and using the reinsertion time to determine whether the sensor has exceeded a predetermined maximum removal time limit.

2. The CGM system of claim 1 , wherein an external device, a transmitter unit, or a cloud-based service comprises the second memory.

3. The CGM system of claim 1 , wherein an external device or transmitter unit comprises the processor.

4. The device further comprises a CGM device configured to be worn by a user, the CGM device comprising: the sensor unit; 2. The CGM system of claim 1, further comprising: a transmitter unit electrically connected to the sensor unit, the transmitter unit comprising a wireless transmitter, the real-time clock, and a microcontroller comprising the processor.

5. The CGM system of claim 4 , wherein the sensor unit and the transmitter unit are integrally formed.

6. 5. The CGM system of claim 4, wherein the sensor unit is replaceable and detachable from the transmitter unit so that it can be reused with other sensor units.

7. 2. The CGM system of claim 1, wherein the processor is further configured to execute computer instructions to stop operation of the CGM in response to the sensor exceeding the predetermined maximum removal time limit.

8. The processor: storing the identifier and the insertion timestamp in the second memory; or 10. The CGM system of claim 1, further configured to execute computer instructions to read sensor data from the sensor unit and estimate a glucose level in response to determining that the sensor has not exceeded the predetermined maximum removal time limit and has not met the maximum insertion time limit.

9. The CGM system of claim 1 , wherein the processor is further configured to execute computer instructions to periodically update the elapsed insertion time of the sensor using the real-time clock.

10. 10. The CGM system of claim 9, wherein the processor is further configured to execute computer instructions to determine, in response to an updated elapsed insertion time, whether the sensor has met or exceeded a predetermined maximum insertion time limit.

11. The CGM system of claim 1 , wherein the processor is further configured to execute computer instructions to determine whether the sensor has been removed from the user's skin surface.

12. 12. The CGM system of claim 11, wherein the processor is further configured to execute computer instructions to store a removal timestamp in the second memory in response to determining that the sensor has been removed from the skin surface of the user.

13. 1. A continuous glucose monitoring (CGM) system comprising: a sensor configured to be inserted into the user's skin and to generate an electrical signal indicative of a glucose level; a first memory having an identifier stored therein that identifies the sensor; a second memory configured to store therein a plurality of sensor identifiers; A real-time clock and a processor in communication with the first and second memories and the real time clock, the processor comprising: reading the identifier stored in the first memory; determining whether the identifier matches any previously stored identifier in the second memory; responsive to the identifier not matching any previously stored identifier in the second memory, storing the identifier and an insertion timestamp in the second memory, wherein the real time clock is used to generate the insertion timestamp; responsive to the identifier matching an identifier previously stored in the second memory, obtaining a reinsertion time using the real time clock; and using the reinsertion time to determine whether the sensor has exceeded a predetermined maximum removal time limit.

14. 14. The CGM system of claim 13, wherein a CGM device comprises the first memory and an external device comprises the second memory, the real-time clock, and the processor, or the first memory comprises a sensor unit memory of a sensor unit and the sensor unit comprises the sensor.

15. The CGM system of claim 13 , wherein the first memory or the second memory is cloud-based.

16. 1. A method for tracking insertion and removal times of a continuous glucose monitoring (CGM) sensor, comprising: In response to activation of the CGM, reading an identifier of the sensor from a sensor unit memory via a processor executing computer instructions; determining whether the identifier matches any previously stored identifier in a second memory; storing the identifier and an insertion timestamp in the second memory in response to the identifier not matching any previously stored identifier in the second memory; and obtaining a reinsertion time in response to the identifier matching a previously stored identifier in the second memory; and using the reinsertion time to determine whether the sensor has exceeded a predetermined maximum removal time limit; ceasing operation of the CGM in response to determining that the sensor has exceeded the predetermined maximum removal time limit.

17. 17. The method of claim 16, wherein determining whether the sensor has exceeded a predetermined removal time limit comprises calculating an elapsed removal time based on the reinsertion time and a previously stored removal timestamp.

18. storing the identifier and the insertion timestamp in the second memory; or 17. The method of claim 16, further comprising, in response to determining that the sensor has not exceeded the predetermined maximum removal time limit and has not met the maximum insertion time limit, reading sensor data via the sensor and estimating a glucose level via the processor.

19. 20. The method of claim 18, further comprising periodically updating an elapsed insertion time of the sensor in response to the reading of the sensor data and the estimating of the glucose level.

20. 20. The method of claim 19, further comprising determining whether the sensor has met or exceeded a predetermined maximum insertion time limit in response to the updating of the elapsed insertion time.

21. 21. The method of claim 20, further comprising ceasing operation of the CGM in response to determining that the sensor has met or exceeded a predetermined maximum insertion time limit.

22. The method of claim 16 , further comprising determining whether the sensor has been removed from the user's skin surface.

23. 23. The method of claim 22, further comprising, in response to determining that the sensor has been removed from the skin surface of the user, storing a removal timestamp in the second memory.

24. 24. The method of claim 23, further comprising updating an elapsed insertion time of the sensor in response to the storing the timestamp.

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