FHIR R4 Observation example: blood pressure

Blood pressure is one Observation with two components, not two separate Observations. The panel code is LOINC 85354-9; each component has its own LOINC code and a quantity in mm[Hg].

The Observation in JSON

{
  "resourceType": "Observation",
  "id": "blood-pressure",
  "status": "final",
  "category": [
    {
      "coding": [
        {
          "system": "http://terminology.hl7.org/CodeSystem/observation-category",
          "code": "vital-signs",
          "display": "Vital Signs"
        }
      ]
    }
  ],
  "code": {
    "coding": [
      {
        "system": "http://loinc.org",
        "code": "85354-9",
        "display": "Blood pressure panel with all children optional"
      }
    ],
    "text": "Blood pressure"
  },
  "subject": {
    "reference": "Patient/example",
    "display": "Jane Doe"
  },
  "effectiveDateTime": "2026-10-01T08:30:00-05:00",
  "component": [
    {
      "code": {
        "coding": [
          {
            "system": "http://loinc.org",
            "code": "8480-6",
            "display": "Systolic blood pressure"
          }
        ]
      },
      "valueQuantity": {
        "value": 128,
        "unit": "mmHg",
        "system": "http://unitsofmeasure.org",
        "code": "mm[Hg]"
      }
    },
    {
      "code": {
        "coding": [
          {
            "system": "http://loinc.org",
            "code": "8462-4",
            "display": "Diastolic blood pressure"
          }
        ]
      },
      "valueQuantity": {
        "value": 82,
        "unit": "mmHg",
        "system": "http://unitsofmeasure.org",
        "code": "mm[Hg]"
      }
    }
  ]
}

Validator result: raw JSON · open the validator

informationNo errors: this Observation matches the FHIR R4 structure checked here.

The elements that matter

Element	Cardinality	Notes
`status`	1..1	Required; `final` for a confirmed measurement.
`category`	0..*	`vital-signs` from the observation-category code system.
`code`	1..1	What was measured: LOINC 85354-9 for the panel.
`subject`	0..1	The patient; optional in base R4, required by most profiles and by Anpheros.
`effectiveDateTime`	0..1	When it was measured; a time needs a time zone.
`component`	0..*	One entry per value, each with its own `code` and `valueQuantity`.

The FHIR vital signs profile asks for the panel code, both components and UCUM units; the structure check here does not enforce that profile.

The full definition is in the FHIR R4 Observation specification.

Common mistakes and the errors they cause

Missing status

Observation.status is 1..1.

errorObservation.statusRequired element is missing.

Time without a time zone

A dateTime with hours needs Z or an offset; a space instead of T also fails.

errorObservation.effectiveDateTimeNot a FHIR dateTime: YYYY, YYYY-MM, YYYY-MM-DD or YYYY-MM-DDThh:mm:ss with a time zone (Z or +hh:mm).

Missing code

Observation.code is 1..1: every observation says what it measured.

errorObservation.codeRequired element is missing.

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More examples

Related guides

How to store medical records using FHIR R4Tutorial: create a Patient, a blood-pressure Observation and a Condition, use a transaction, search, update with history and read provenance — every request with curl and the real response, on the free sandbox.
How to normalize medical dataTutorial: turn medical data from many sources into one comparable form — LOINC and ATC lookup, UCUM units, ISO dates, reference ranges, no duplicates on retry, and validation against the European lab profile.