Endpoint DeviceMetric

This document describes the syntax and semantics of querying FHIR DeviceMetric resources via the standard FHIR RESTful API. A DeviceMetric resource represents a status instance of a medical aid or implant, and MAY be referenced by a measurement. In the context of HDDT, a DeviceMetric represents the calibration status of a medical aid or implant.

To be compliant with § 374a SGB V, a Device Data Recorder MUST implement interactions for reading and searching DeviceMetric resources:

• reading individual DeviceMetric resources that are referenced by Observation resources.
• version specific reading individual DeviceMetric resources that are referenced by Observation resources. This interaction MAY be omitted by a Device Data Recorder if it does not support versioning of DeviceMetric resources (see Retrieving Data for a discussion on how to express changes of the calibration state of a sensor).
• searching for DeviceMetric resources linked with the current patient and an authorised MIV.

Returned resources MUST conform to the HDDT Sensor Type and Calibration Status DeviceMetric profile.

Endpoints

DeviceMetric - READ

DeviceMetric - VREAD

Remark: A Device Data Recorder MAY omit the version specific read interaction if it does not support versioning of DeviceMetric resources (see Retrieving Data for a discussion on how to express changes of the calibration state of a sensor).

DeviceMetric - SEARCH

Remark: The FHIR specification allows searching for resources by various parameters. However, in the context of HDDT, the only relevant search parameter is the patient who is associated with the access token. Therefore, the search interaction is restricted to this parameter only.

Profile - HDDT Sensor Type and Calibration Status

Profile: DeviceMetric – Sensor Type and Calibration Status

This structure is derived from DeviceMetric

Name	Flags	Card.	Type	Description & Constraints    Filter: Bindings Constraints Obligations
DeviceMetric		0..*	DeviceMetric	Configuration or setting capability of a personal health device
implicitRules	?!Σ	0..1	uri	A set of rules under which this content was created
modifierExtension	?!	0..*	Extension	Extensions that cannot be ignored
type	Σ	1..1	CodeableConcept	Identity of metric, for example Heart Rate or PEEP Setting Binding: DeviceMetricAndComponentTypes (preferred): Describes the metric type.
unit	Σ	0..1	CodeableConcept	UCUM code of the unit of the measurement as it is used when presenting data to the patient Binding: UCUMCodes (required): For HDDT only codes from UCUM MUST be used for coding units of measurements
source	Σ	1..1	Reference(Device – Personal Health Device)	Reference to the Personal Health Device holding the sensor
operationalStatus	Σ	0..1	code	on | off | standby | entered-in-error Binding: DeviceMetricOperationalStatus (required): Describes the operational status of the DeviceMetric.
category	Σ	1..1	code	measurement | setting | calculation | unspecified Binding: DeviceMetricCategory (required): Describes the category of the metric.
calibration	SΣ	0..*	BackboneElement	Describes the calibrations that have been performed or that are required to be performed
modifierExtension	?!Σ	0..*	Extension	Extensions that cannot be ignored even if unrecognized
state	Σ	1..1	code	not-calibrated | calibration-required | calibrated | unspecified Binding: DeviceMetricCalibrationState (required): Describes the state of a metric calibration.
time	SΣ	0..1	instant	Time when the last calibration has been performed
Documentation for this format

Example: Glucometer DeviceMetric

In this example the patient uses a glucometer that is connected to the Device Data Recorder via Bluetooth. The glucometer is used to perform blood glucose measurements that are stored as Observation resources in the Device Data Recorder. Each Observation references the DeviceMetric resource that holds the calibration state of the glucometer.

In the given example the device measures the glucose concentration from capillary blood by using test strips. The patient’s preferred unit is mg/dl which is used by the device for displaying measured values. The glucometer needs to be calibrated by the patient using control strips. The last calibration was performed in Septemer 2025 and the glucometer is still calibrated.

Remarks:

• The text element is omitted in this example to keep the example small. Nevertheless, as all HDDT resources are intended for sole machine processing, the text element MAY be omitted.

DeviceMetric - READ

Request: GET /DeviceMetric/example-glucometer-metric

Response:

{
  "resourceType" : "DeviceMetric",
  "id" : "example-glucometer-metric",
  "meta" : {
    "profile" : [
      🔗 "https://gematik.de/fhir/hddt/StructureDefinition/hddt-sensor-type-and-calibration-status"
    ]
  },
  "type" : {
    "coding" : [
      {
        "system" : "urn:iso:std:iso:11073:10101",
        "version" : "20250520",
        "code" : "160184",
        "display" : "MDC_CONC_GLU_CAPILLARY_WHOLEBLOOD"
      }
    ]
  },
  "unit" : {
    "coding" : [
      {
        "system" : "http://unitsofmeasure.org",
        "code" : "mg/dL",
        "display" : "mg/dL"
      }
    ]
  },
  "source" : {
    🔗 "reference" : "Device/example-glucometer"
  },
  "operationalStatus" : "on",
  "category" : "measurement",
  "calibration" : [
    {
      "type" : "gain",
      "state" : "calibrated",
      "time" : "2025-09-01T09:08:04+02:00"
    }
  ]
}

DeviceMetric - SEARCH

Request: GET /DeviceMetric

Response:

{
    "resourceType": "Bundle",
    "type": "searchset",
    "entry": [
        {
            "fullUrl": "https://example.com/fhir/DeviceMetric/example-glucometer-metric",
            "resource": {
                "resourceType": "DeviceMetric",
                "id": "example-glucometer-metric",
                "meta": {
                    "profile": [
                        "https://gematik.de/fhir/hddt/StructureDefinition/hddt-sensor-type-and-calibration-status"
                    ]
                },
                "type": {
                    "coding": [
                        {
                            "code": "160184",
                            "system": "urn:iso:std:iso:11073:10101",
                            "version": "20250520",
                            "display": "MDC_CONC_GLU_CAPILLARY_WHOLEBLOOD"
                        }
                    ]
                },
                "unit": {
                    "coding": [
                        {
                            "code": "mg/dL",
                            "system": "http://unitsofmeasure.org",
                            "display": "mg/dL"
                        }
                    ]
                },
                "source": {
                    "reference": "Device/example-glucometer"
                },
                "operationalStatus": "on",
                "category": "measurement",
                "calibration": [
                    {
                        "type": "gain",
                        "state": "calibrated",
                        "time": "2025-09-01T09:08:04+02:00"
                    }
                ]
            },
            "search": {
                "mode": "match"
            }
        }
    ]
}

Example: rtCGM DeviceMetric

In this example, the patient uses a real-time continuous glucose monitor (rtCGM) that is connected to the Device Data Recorder via Bluetooth. The rtCGM continuously measures the glucose concentration in interstitial fluid, and the resulting data are stored as Observation resources in the Device Data Recorder. Each Observation references a DeviceMetric resource that represents the calibration status of the rtCGM.

The example device measures the glucose concentration from interstitial fluid with a frequency of one measurement every three minutes. The patient’s preferred unit is mg/dl. The device is calibrated by the manufacturer and does not require user calibration.

Instance of the HDDT Sensor Type and Calibration Status profile

{
    "resourceType": "Bundle",
    "type": "searchset",
    "entry": [
        {
            "fullUrl": "https://example.com/fhir/DeviceMetric/example-devicemetric-cgm",
            "resource": {
                "resourceType": "DeviceMetric",
                "id": "example-devicemetric-cgm",
                "meta": {
                    "profile": [
                        "https://gematik.de/fhir/hddt/StructureDefinition/hddt-sensor-type-and-calibration-status"
                    ]
                },
                "type": {
                    "coding": [
                        {
                            "code": "160212",
                            "system": "urn:iso:std:iso:11073:10101",
                            "version": "20250520",
                            "display": "MDC_CONC_GLU_ISF"
                        }
                    ]
                },
                "unit": {
                    "coding": [
                        {
                            "code": "mg/dL",
                            "system": "http://unitsofmeasure.org",
                            "display": "mg/dL"
                        }
                    ]
                },
                "source": {
                    "reference": "Device/example-device-cgm"
                },
                "operationalStatus": "on",
                "category": "measurement",
                "measurementPeriod": {
                    "repeat": {
                        "frequency": 1,
                        "period": 3,
                        "periodUnit": "min"
                    }
                },
                "calibration": [
                    {
                        "type": "unspecified",
                        "state": "calibrated"
                    }
                ]
            },
            "search": {
                "mode": "match"
            }
        }
    ]
}