Bluetooth GATT Characteristic Reference

CGM Measurement (0x2AA7)

org.bluetooth.characteristic.cgm_measurement

The CGM Measurement characteristic is a variable length structure containing one or more CGM Measurement records, each comprising a Size field, a Flags Field, a Glucose Concentration field, a Time Offset field, a Sensor Status Annunciation field (optional), a CGM Trend Information Field (optional), a CGM Quality Field (optional), and an E2E-CRC Field (mandatory if this feature is supported).

Quick Summary

Payload length is profile-defined or variable based on field formats. This page is generated from official GATT XML and presented as implementation-ready guidance.

At a Glance

Key reference details for BLE implementation, interoperability testing, and AI-assisted troubleshooting.

Property	Value
Name	CGM Measurement
UUID	0x2AA7
Type	org.bluetooth.characteristic.cgm_measurement
XML Root	Characteristic
Source File	org.bluetooth.characteristic.cgm_measurement.xml
Field Count	8

Field Specification

Parsed field definitions from the source XML value structure.

Field	Requirement	Format	Unit	Exponent	Notes
Size	Mandatory	uint8	-	-	The Size Field represents the size of the CGM Measurement record. In minimum the size is 6 octets and is enlarged by more octets indicated by the Flags Field (Sensor Status Annunciation Field, CGM Trend Information Field and CGM Quality Field) and the E2E-CRC Supported bit in CGM Feature. The Size Field itself is included in the overall length calculation.
Flags	Mandatory	8bit	-	-	-
CGM Glucose Concentration	Mandatory	SFLOAT	org.bluetooth.unit.mass_density.milligram_per_decilitre	0	The CGM Glucose Concetration Field contains the CGM glucose concentration in mg/dL as a SFLOAT data type. The SFLOAT-Type is a 16-bit word comprising a signed 4-bit integer exponent followed by a signed 12-bit Mantissa, each in twos-complement form.
Time Offset	Mandatory	uint16	org.bluetooth.unit.time.minute	0	The following values are defined for the Time Offset Field, specifying the relative time difference of the single CGM values to the session start time. Value: (0x0000 - 0xFFFF), Description: (Time offset in minutes as offset to the Session Start Time).
Sensor Status Annunciation	C4	variable	-	-	The Sensor Status Annunciation Field is an optional field comprising up to three octets. It is only attached if one or more bits are set to ?1?. Only the affected octet(s) shall be added and indicated by the Flags Field. The Sensor Status Annunciation Field shall be attached to every CGM Measurement Record to which the status applies.
CGM Trend Information	C1	SFLOAT	org.bluetooth.unit.mass_density.milligram_per_decilitre	0	The CGM Trend Information Field contains the CGM Trend information in (mg/dL)/min as an SFLOAT data type. This field is optional if the device supports CGM Trend information (Bit 15 in CGM Feature is set to 1) otherwise excluded.
CGM Quality	C2	SFLOAT	org.bluetooth.unit.percentage	0	This field contains the CGM Quality information in % as an SFLOAT data type. The SFLOAT-Type is a 16-bit word comprising a signed 4-bit integer exponent followed by a signed 12-bit Mantissa, each in twos-complement form. This field is optional if the device supports CGM Quality (Bit 16 in CGM Feature is set to 1) otherwise excluded.
E2E-CRC	C3	uint16	-	-	If the device supports E2E-safety (E2E-CRC Supported bit is set in CGM Feature), the measurement is secured by a CRC calculated over all fields. The computation of the CRC is done using a CRC-CCITT generator polynomial g(D)=D16+D12+D5+1 (i.e.210041 in octal representation) with a seed of 0xFFFF. This field is mandatory if the device supports E2E-CRC (Bit 12 in CGM Feature is set to 1) otherwise excluded.

Bit Map

Bit-level enumerations extracted from the XML BitField definition.

Field	Bit	Size	Name	0 Means	1 Means
Flags	0	1	CGM Trend Information Present	False	True
Flags	1	1	CGM Quality Present	False	True
Flags	5	1	Sensor Status Annunciation Field, Warning-Octet present	False	True
Flags	6	1	Sensor Status Annunciation Field, Cal/Temp-Octet present	False	True
Flags	7	1	Sensor Status Annunciation Field, Status-Octet present	False	True
Sensor Status Annunciation	0	1	Session Stopped	False	True
Sensor Status Annunciation	1	1	Device Battery Low	False	True
Sensor Status Annunciation	2	1	Sensor type incorrect for device	False	True
Sensor Status Annunciation	3	1	Sensor malfunction	False	True
Sensor Status Annunciation	4	1	Device Specific Alert	False	True
Sensor Status Annunciation	5	1	General device fault has occurred in the sensor	False	True
Sensor Status Annunciation	8	1	Time synchronization between sensor and collector required	False	True
Sensor Status Annunciation	9	1	Calibration not allowed	False	True
Sensor Status Annunciation	10	1	Calibration recommended	False	True
Sensor Status Annunciation	11	1	Calibration required	False	True
Sensor Status Annunciation	12	1	Sensor Temperature too high for valid test/result at time of measurement	False	True
Sensor Status Annunciation	13	1	Sensor temperature too low for valid test/result at time of measurement	False	True
Sensor Status Annunciation	16	1	Sensor result lower than the Patient Low level	False	True
Sensor Status Annunciation	17	1	Sensor result higher than the Patient High level	False	True
Sensor Status Annunciation	18	1	Sensor result lower than the Hypo level	False	True
Sensor Status Annunciation	19	1	Sensor result higher than the Hyper level	False	True
Sensor Status Annunciation	20	1	Sensor Rate of Decrease exceeded	False	True
Sensor Status Annunciation	21	1	Sensor Rate of Increase exceeded	False	True
Sensor Status Annunciation	22	1	Sensor result lower than the device can process	False	True
Sensor Status Annunciation	23	1	Sensor result higher than the device can process	False	True

Byte Layout and Decode

Payload length is profile-defined or variable based on field formats.

function decodePayload(dataView, offset = 0) {
  const size = dataView.getUint8(offset + 0);
  // Parse flags (8bit) according to Bluetooth format rules.
  // Parse cgm_glucose_concentration (SFLOAT) according to Bluetooth format rules.
  const time_offset = dataView.getUint16(offset + 1, true);
  // Parse sensor_status_annunciation (variable) according to Bluetooth format rules.
  // Parse cgm_trend_information (SFLOAT) according to Bluetooth format rules.
  // Parse cgm_quality (SFLOAT) according to Bluetooth format rules.
  const e2e_crc = dataView.getUint16(offset + 3, true);
  return { size, flags, cgm_glucose_concentration, time_offset, sensor_status_annunciation, cgm_trend_information };
}

Use Cases and Integration Notes

BLE Telemetry

Map characteristic values into dashboards and alerts for device observability.

Firmware Regression

Compare decoded fields across builds to detect protocol or scaling changes.

App Integration

Build stable parsing paths that convert raw payloads into typed app models.

Implementation Checklist

Validate payload length and mandatory fields before decode.
Decode with Bluetooth-specified signedness, unit, and exponent handling.
Convert units at presentation boundaries to avoid drift in business logic.
Persist raw packets and decoded values for reproducible troubleshooting.

FAQ

What is CGM Measurement in Bluetooth GATT?

CGM Measurement is defined as a Bluetooth GATT characteristic entry with type org.bluetooth.characteristic.cgm_measurement and UUID 0x2AA7.

What UUID identifies CGM Measurement?

The UUID for CGM Measurement is 0x2AA7.

How should I parse CGM Measurement?