Glucose Service

The Flags field shall be included in the Glucose Measurement characteristic.

The Flags field is an 8-bit bit field which indicates the unit used in the Glucose Concentration field (if used), what fields are present in the Glucose Measurement characteristic, and whether or not context information is included.

If a Glucose Measurement characteristic includes contextual information (i.e., a corresponding Glucose Measurement Context characteristic), the Context Information Follows Flag (bit 4 of the Flags field) shall be set to 1, otherwise the Flag shall be set to 0.

Bits defined as Reserved for Future Use (RFU) in the Flags field in [3] shall be set to 0.

The Sequence Number field shall be included in the Glucose Measurement characteristic.

The Sequence Number is an unsigned 16-bit integer that represents the chronological order of the patient records in the Server measurement database. The initial default value shall be 0x0000. The Sequence Number assigned to each Glucose Measurement characteristic value is used to maintain chronological order of patient records. The use of Base Time and Time Offset for this purpose cannot be relied upon due to the potential for user induced date and time errors or catastrophic time base errors that may occur due to a battery failure.

It is recommended that the last Sequence Number used is stored in non-volatile memory to ensure a continuum in case of a reset or battery failure. In addition the Sequence Number shall not be reset back to the default when the database is cleared through the Delete Stored Records procedure discussed in Section 3.4.3.3.

The Sequence Number shall be incremented by 1 for each successive Glucose Measurement characteristic value. The maximum value for Sequence Number permitted is 0xFFFF. Assuming a high use of 8 times per day, the maximum value of the Sequence Number would be reached in ~22 years. Since product life expectancy of a Glucose Sensor is ~ 5 years, this value significantly exceeds that expectation. This value is not permitted to roll over, although a reset of the Sequence Number back to zero might occur due to non-volatile memory failure or other catastrophic hardware or software errors within the Sensor.

Note that some gaps in sequence numbers may exist in the internal storage of a Server in some situations. For example, this can occur if the user locally deleted one or more entries at the user interface or if a Client deleted some entries using the Delete Stored Records command via the Record Access Control Point.

Note that the value of a sequence number in the Glucose Measurement characteristic shall not be changed due to e.g. patient record deletions or other actions.

The Base Time field shall be included in the Glucose Measurement characteristic value.

The Base Time field represents the value of an internal real-time clock or equivalent that keeps time relative to its initial setting in resolution of seconds. Its initial value is typically set at the time of manufacturing or upon first use by the end user. The Server’s internal Base Time is not intended to be updated by the user or via an external time service (e.g. the Current Time Service [5]) except in the case of an unrecoverable loss of Base Time in the Server caused by clock reset, corruption or other hardware or software failures.

Maintaining a Base Time is significant because it is clinically important to maintain the date/time continuum of patient records with a contiguous, uninterrupted Base Time. Refer to the next section for a description of the use of Time Offset to control the user-facing time.

The Base Time field is defined to use the same format as the Date Time characteristic defined in [3]. However, a value of 0 for the year, month or day fields shall not be used for this service.

The Time Offset field shall be included in the Glucose Measurement characteristic value whenever the value of the Time Offset changes from the last reported measurement. Otherwise, it may be included even if the value does not change from patient record to patient record. See also Section 3.4.3.4 for requirements related to the use of this field in the first transmitted patient record when using the Record Access Control Point.

The default value of this field is 0x0000. The implementation may restrict the user from entering time values via the user interface that would alter the Time Offset value outside the range of +/- 24 hours to avoid entering incorrect time values e.g. wrong day due to user entry error.

If the Time Offset field is present in the Glucose Measurement characteristic, bit 0 of the Flags field is set to 1; otherwise bit 0 of the Flags field is set to 0.

The Time Offset field is used in conjunction with the Base Time field to represent the user-facing date and time at the time of measurement.

The Time Offset field is defined as a 16-bit signed integer representing the number of minutes the user-facing time differs from the Base Time.

The user-facing time (i.e., the time of measurement with respect to the user of the device) is the sum of the Base Time and the Time Offset. The Time Offset component of the user-facing time of the device may be updated by various means such as via a simple user interface on the device or via the Current Time Service [5]. When the user-facing time is updated under normal operating conditions, only the Time Offset component shall be changed and the Base Time component shall not be changed. See Section 3.1.1.3 for additional information.

The Glucose Concentration field is optional, but if it is present, the Type-Sample Location field shall also be present.

The Type nibble and the Sample Location nibble comprise one octet. Therefore, when one nibble is present, both nibbles shall be present.

If the Glucose Concentration field and the Type-Sample Location field are present, bit 1 of the Flags field is set to 1; otherwise bit 1 of the Flags field is set to 0.

If a value for the Glucose Concentration field is unavailable (e.g. due to an invalid result from a computation step or missing data due to the hardware’s inability to provide a valid measurement), the special short float value NaN (see section 4) defined in ISO/IEEE 11073-20601a [4] shall be used.

If the unit of the Glucose Concentration is in base units of kg/L (typically displayed in units of mg/dL), bit 2 of the Flags field is set to 0. Otherwise, the unit is in base units of mol/L (typically displayed in units of mmol/L) and bit 2 of the Flags field is set to 1. Note that the base units defined in [3] correspond to units of kg/L and mol/L respectively. When preparing the SFLOAT value, the SFLOAT exponent of the Glucose Concentration value needs to be adjusted to correspond to the base values. For example, when a Glucose Concentration value in units of mg/dL is converted to units of kg/L, the SFLOAT exponent will need to be adjusted by subtracting 5. Similarly, when a Glucose Concentration value in units of mmol/L is converted to units of mol/L, the SFLOAT exponent will need to be adjusted by subtracting 3.

The Sensor Status Annunciation field may be included in the Glucose Measurement characteristic value if the device supports Sensor Status Annunciation flags.

If the Sensor Status Annunciation field is present in the Glucose Measurement characteristic value, bit 3 of the Flags field is set to 1; otherwise bit 3 of the Flags field is set to 0.

Refer to the Glucose Feature characteristic (Section 3.3) for a description of the inter-relationship between the bits in this field and the bits in the Glucose Feature characteristic.

Bits defined as Reserved for Future Use (RFU) in the Sensor Status Annunciation field in [3] shall be set to 0.

The Client Characteristic Configuration descriptor shall be included in the Glucose Measurement characteristic.

The Flags field shall be included in the Glucose Measurement Context characteristic.

Bits defined as Reserved for Future Use (RFU) in the Flags field in [3] shall be set to 0.

The Sequence Number field shall be included in the Glucose Measurement Context characteristic.

The Sequence Number value shall be the same as the value of the Sequence Number of its corresponding Glucose Measurement characteristic. This is used to ensure the Glucose Measurement Context characteristic is matched to the appropriate Glucose Measurement characteristic and add further robustness to the service.

The Extended Flags field is optional. The existence of the Extended Flags field is indicated by setting bit 7 of the Flags field.

Bits defined as Reserved for Future Use (RFU) in the Extended Flags field in [3] shall be set to 0.

The Carbohydrate ID field and the Carbohydrate field are optional, but when one is used, both shall be used.

If the Carbohydrate ID field and Carbohydrate field are present in the Glucose Measurement Context characteristic, bit 0 of the Flags field is set to 1; otherwise bit 0 of the Flags field is set to 0.

The Meal field is optional.

If the Meal field is present in the Glucose Measurement Context characteristic, bit 1 of the Flags field is set to 1; otherwise bit 1 of the Flags field is set to 0.

The Tester-Health field is optional. The Tester nibble and the Health nibble comprise one octet. Therefore, when one nibble is present, both nibbles shall be present.

If the Tester-Health field is present in the Glucose Measurement Context characteristic, bit 2 of the Flags field is set to 1; otherwise bit 2 of the Flags field is set to 0.

The Exercise Duration field and the Exercise Intensity are optional, but when one is used, both shall be used.

If the Exercise Duration field and the Exercise Intensity field are present in the Glucose Measurement Context characteristic, bit 3 of the Flags field is set to 1; otherwise bit 3 of the Flags field is set to 0.

Since Exercise Duration is a 16 bit unsigned integer, the highest value that can be represented is 65535 seconds (0xFFFF). If the maximum value of 65535 seconds (equivalent to 18 hours) is attained, the field value should remain at 0xFFFF so the Client can be made aware that the maximum value has been reached.

The Medication ID field and the Medication field are optional, but when one is used, both shall be used.

If the Medication ID field and Medication field are present in the Glucose Measurement Context characteristic, bit 4 of the Flags field is set to 1; otherwise bit 4 of the Flags field is set to 0.

If the unit of the Medication is in base units of kilograms (typically entered by the user in units of milligrams), bit 5 of the Flags field is set to 0. Otherwise, the unit is in base units of liters (typically entered by the user in units of milliliters) and bit 5 of the Flags field is set to 1. Note that the base units defined in [3] corresponds to the units above are kilograms and liters respectively. When preparing the SFLOAT value, the SFLOAT exponent of the Medication value needs to be adjusted to correspond to the base values. For example, when a Medication value in units of milligrams is converted to units of kilograms, the SFLOAT exponent will need to be adjusted by subtracting 6.

The HbA1c field is optional.

If the HbA1c field is present in the Glucose Measurement Context characteristic, bit 6 of the Flags field is set to 1; otherwise bit 6 of the Flags field is set to 0.

The Client Characteristic Configuration descriptor shall be included in the Glucose Measurement Context characteristic.

Since the value of the Operand is defined per service, when the RACP is used with the Glucose Service, a Filter Type field is defined to enable the flexibility to filter based on different criteria (i.e., Sequence Number or optionally User Facing Time).

Some Procedure Operators (i.e., less than or equal to, greater than or equal to and within range of) require a Filter Type as part of the Operand. This is used to specify the field in the Glucose Measurement characteristic value that is used to perform the filtering. When used, the Filter Type byte shall always precede the applicable filter parameter(s) within the Operand. For example, when used with the ‘within range of’ Operator, the Operand has the format <Filter Type><minimum><maximum> where Filter Type is the Least Significant Octet of the Operand. See Table 3.4 for a list of valid Filter Type values.

When using the Sequence Number Filter Type, the format of the Operand is the Sequence Number Filter Type value followed by the applicable Sequence Number value or value pair depending upon the Operator.

When using the User Facing Time Filter Type, the format of the Operand is the User Facing Time Filter Type value followed by the applicable User Facing Time (sum of the Base Time and the Time Offset) value or value pair depending upon the Operator.

When the Report Number of Stored Records Op Code is written to the Record Access Control Point, the Server shall calculate and respond with a record count in UINT16 format based on filter criteria, Operator and Operand values. Refer to Table 3.3 for Operand requirements when used with a specific Operator and note that in some cases, no Operand is used. The record count reported in the response is calculated based on the current state of the sensor database, and may change between connections or after records are cleared. The response is indicated using the Number of Stored Records Response Op Code. If the operation results in an error condition, this shall be indicated using the Response Code Op Code and the appropriate Response Code Value in the Operand for the error condition.

If the Server does not locate any records matching the filter criteria of the request, the Server shall indicate the Record Access Control Point with a Number of Stored Records Response Op Code and the Operand set to 0x0000.

If the operation results in an error condition, this shall be indicated using the Response Code Op Code and the appropriate Response Code Value in the Operand for the error condition.

When the Delete Stored Records Op Code is written to the Record Access Control Point, the Server may delete the specified patient records based on Operator and Operand values. Deletion of records is considered to be a permanent deletion of records from the patient database. Refer to Table 3.3 for Operand requirements when used with a specific Operator and note that in some cases, no Operand is used. Due to the sensitivity of the data, it is permitted for Sensors to only allow their data to be deleted by specific Clients.

The Server shall indicate this characteristic with a Response Code Value of Success if the records were successfully deleted from the patient record database.

If the Server does not locate any records matching the filter criteria of the request, the Server shall indicate the Record Access Control Point with a Response Code Op Code and Response Code Value in the Operand set to No Records Found.

If the operation results in an error condition, this shall be indicated using the Response Code Op Code and the appropriate Response Code Value in the Operand for the error condition.

When the Report Stored Records Op Code is written to the Record Access Control Point, the Server shall notify the selected set of stored patient records based on the filter criteria specified in the Operator and Operand. Refer to Table 3.3 for Operand requirements when used with a specific Operator and note that in some cases, no Operand is used. The semantics of a record transfer is a ‘copy’ of the records and not a ‘move’ of the records.

The transfer of a patient record shall include a notification of the Glucose Measurement characteristic, and if context information exists in the patient record (based on the Context Information Flag of the Glucose Measurement characteristic value), the notification of the Glucose Measurement characteristic shall be followed by a notification of the Glucose Measurement Context characteristic.

The Time Offset field (described in Section 3.1.1.4) shall be included in the first transmitted Glucose Measurement characteristic and also in subsequent records whenever values changes to the Time Offset field occur. Otherwise, the Time Offset field is optional.

If during the record transfer a new patient record becomes available (i.e., after the Report Stored Records procedure is initiated), the Sensor may include this new record in the measurement transfer. A profile using this service is required to ensure Clients are tolerant of the possibility that one additional record is received than might have been expected.

Once all data records for a given request have been notified by the Server, the Server shall indicate the Record Access Control Point with a Response Code Op Code and Response Code Value in the Operand set to Success.

If the Server does not locate any records matching the filter criteria of the request, the Server shall indicate the Record Access Control Point with a Response Code Op Code and Response Code Value in the Operand set to No Records Found.

If the operation results in an error condition, this shall be indicated using the Response Code Op Code and the appropriate Response Code Value in the Operand for the error condition.

If the Server is required to interrupt its data transfer before completion for any reason, the Server shall indicate the Record Access Control Point with a Response Code Op Code and Response Code Value in the Operand set to Procedure not completed.

When the Abort Operation Op Code is written to the Record Access Control Point, the Server shall stop any RACP procedures currently in progress and shall make a best effort to stop sending any further data.

Once all RACP procedures have been stopped, the Server shall indicate the Record Access Control Point with a Response Code Op Code and Response Code Value in the Operand set to Success.

If the operation results in an error condition, this shall be indicated using the Response Code Op Code and the appropriate Response Code Value in the Operand for the error condition.

The Client Characteristic Configuration descriptor shall be included in the Record Access Control Point characteristic.