# Continuous Blood Glucose (`cbg`)

## Quick Summary

## Type (`type`)

This is the Tidepool data type for continuous glucose monitor sensor data. "CBG" is an abbreviation of "continuous blood glucose" and contrasts with "SMBG," abbreviating "self-monitored blood glucose." SMBG is the Tidepool data type for traditional fingerstick blood glucose meter data.

The device time field is only optional for *this* data type. This is because Tidepool is now ingesting Dexcom G5 and G6 data via integration with Apple's HealthKit, which only stores a UTC-anchored timestamp and does not have "receiver display time" like earlier generations of Dexcom devices.

## Trend Rate Units (`trendRateUnits`)

A continuous glucose monitor may optionally report the trend rate. That is, the rate at which the glucose value has been changing over some period of time, usually on the order of minutes. If this is available then `trendRateUnits` and `trendRate` may be specified to capture this data. Valid values for `trendRateUnits` are `mmol/L/minute` and `mg/dL/minute`.

## Trend Rate (`trendRate`)

A continuous glucose monitor may optionally report the trend rate. That is, the rate at which the glucose value has been changing over some period of time, usually on the order of minutes. If this is available then `trendRateUnits` and `trendRate` may be specified to capture this data. The `trendRate` is a floating point value whose valid range depends upon the `trendRateUnits`. For a `trendRateUnits` of `mmol/L/minute` then the range is from -5.5 to 5.5 and for `mg/dL/minute` it is -100.0 to 100.0.

## Sample Interval (`sampleInterval`)

With the latest generation of continuous glucose monitors, different devices may support different intervals between glucose samples. For example, every 5 minutes or every 15 minutes between glucose samples. In fact, some newer devices may even report multiple sample intervals from different glucose data streams. For example, a device that reports both 1-minute and 5-minutes glucose samples.

In order to distinguish between sample intervals and to assist with accurate statistical calculations, the `sampleInterval` should be specified, if it is known. The value must be an integer representing number of milliseconds between samples for the data stream that a datum belongs to. For example, if a device reports both 1-minute and 5-minute samples, then the upload would contain some `cbg` data with a sample interval of 60000 (milliseconds in 1 minute) and others with a sample interval of 300000 (milliseconds in 5 minutes). The typical sample intervals are 60000 (milliseconds in 1 minute), 300000 (milliseconds in 5 minutes), and 900000 (milliseconds in 15 minutes).

While this field is optional, it is strongly encouraged to provide this field, assuming definitive information regarding sample interval is available from the device.

## Backfilled (`backfilled`)

The backfilled field, an optional boolean, is used to indicate whether this datum was backfilled from the continuous glucose monitor sensor to the device capturing the data. For example, if the CGM sensor is out-of-range of the mobile phone capturing the data, then when the CGM sensor comes back in-range of the mobile phone, the historic sensor data (while the CGM sensor was out-of-range) is "backfilled" to the mobile phone. If it is definitively known that this datum was indeed backfilled, then this field should be set to `true`. If it is definitely known that this datum was **not** backfilled, then this field should be set to `false`. If it is not definitely known one-way-or-the-other, then this field should **not** be specified.

While this field is optional, it is strongly encouraged to provide this field, assuming definitive information regarding backfill is available from the device.

## Examples


```json Example (client)
{
    "type": "cbg",
    "units": "mmol/L",
    "value": 3.996538553552784,
    "trendRate": -0.4,
    "trendRateUnits": "mmol/L/minute",
    "sampleInterval": 300000,
    "clockDriftOffset": 0,
    "conversionOffset": 0,
    "deviceId": "DevId0987654321",
    "deviceTime": "2018-05-14T18:17:07",
    "guid": "82bd8ef1-cfa1-4b49-9230-e2cecac7c5cd",
    "id": "b8858168bd4e447184ee7c7743ffe303",
    "time": "2018-05-14T08:17:07.384Z",
    "timezoneOffset": 600,
    "uploadId": "SampleUploadId"
}
```


```json Example (ingestion)
{
    "type": "cbg",
    "units": "mg/dL",
    "value": 421,
    "trendRate": -2.2,
    "trendRateUnits": "mg/dL/minute",
    "sampleInterval": 60000,
    "clockDriftOffset": 0,
    "conversionOffset": 0,
    "deviceId": "DevId0987654321",
    "deviceTime": "2018-05-14T18:17:07",
    "time": "2018-05-14T08:17:07.385Z",
    "timezoneOffset": 600,
    "uploadId": "SampleUploadId"
}
```


```json Example (storage)
{
    "type": "cbg",
    "units": "mmol/L",
    "value": 27.25417263603357,
    "trendRate": -0.4,
    "trendRateUnits": "mmol/L/minute",
    "sampleInterval": 300000,
    "_active": true,
    "_groupId": "abcdef",
    "_schemaVersion": 0,
    "_version": 0,
    "clockDriftOffset": 0,
    "conversionOffset": 0,
    "createdTime": "2018-05-14T08:17:12.385Z",
    "deviceId": "DevId0987654321",
    "deviceTime": "2018-05-14T18:17:07",
    "guid": "6ad8322a-e29d-4db7-825f-e0ad4c45d723",
    "id": "7779ad3759b14d1fadda7b5bab6d79bd",
    "time": "2018-05-14T08:17:07.385Z",
    "timezoneOffset": 600,
    "uploadId": "SampleUploadId"
}
```

## Keep Reading

* [Annotations](/docs/device-data/annotations)
* [CGM Settings](/docs/device-data/data-types/cgm-settings)
* [Common Fields](/docs/device-data/common-fields)
* [Pump Settings](/docs/device-data/data-types/pump-settings)
* [Self-Monitored Glucose (SMBG)](/docs/device-data/data-types/smbg)
* [Units](/docs/device-data/units)