FHIR Observation Resource (R4)

Observation records a measurement or assertion about a patient: vital signs, laboratory results, social history, survey answers. Element table, search parameters, example JSON and FHIRPath for FHIR R4.

• FHIR Observation Resource (R4) — part of the free FHIR Toolbox library.
• Runs entirely in your browser: your FHIR data is never uploaded to a server.

Overview

Observation records a measurement or assertion about a patient: vital signs, laboratory results, social history, survey answers. What was measured lives in code; the result lives in a value[x] choice element (Quantity, CodeableConcept, string and more). Panels such as blood pressure use component for the individual readings.

Elements

Example JSON (R4)

{
  "resourceType": "Observation",
  "id": "blood-pressure",
  "status": "final",
  "category": [
    {
      "coding": [
        {
          "system": "http://terminology.hl7.org/CodeSystem/observation-category",
          "code": "vital-signs"
        }
      ]
    }
  ],
  "code": {
    "coding": [
      {
        "system": "http://loinc.org",
        "code": "85354-9",
        "display": "Blood pressure panel"
      }
    ]
  },
  "subject": {
    "reference": "Patient/example"
  },
  "effectiveDateTime": "2024-05-01T09:30:00Z",
  "component": [
    {
      "code": {
        "coding": [
          {
            "system": "http://loinc.org",
            "code": "8480-6",
            "display": "Systolic blood pressure"
          }
        ]
      },
      "valueQuantity": {
        "value": 120,
        "unit": "mmHg",
        "system": "http://unitsofmeasure.org",
        "code": "mm[Hg]"
      }
    },
    {
      "code": {
        "coding": [
          {
            "system": "http://loinc.org",
            "code": "8462-4",
            "display": "Diastolic blood pressure"
          }
        ]
      },
      "valueQuantity": {
        "value": 80,
        "unit": "mmHg",
        "system": "http://unitsofmeasure.org",
        "code": "mm[Hg]"
      }
    }
  ]
}

FHIRPath

• Observation.code.coding.where(system='http://loinc.org').code — LOINC code of the observation
• Observation.component.where(code.coding.code='8480-6').value.ofType(Quantity).value — Systolic value from a blood-pressure panel
• Observation.component.value.ofType(Quantity).unit — Units of every component reading
• Observation.effective.ofType(dateTime) — Effective time, narrowed to dateTime with ofType()

Common validation errors

• Using value instead of the concrete choice name. In JSON it is valueQuantity, valueString, valueCodeableConcept and so on, never a bare value.
• Setting more than one value[x]. Only one may be present.
• Omitting status, a required element. Use final, preliminary, amended and so on.
• Quantity without a coded unit. Set system http://unitsofmeasure.org and a UCUM code alongside the human-readable unit.
• Putting a panel's readings in separate top-level Observations without linking them, or forgetting that a panel result belongs in component (or hasMember).

FHIR Toolbox is a free, privacy-first collection of HL7 FHIR utilities by Omindra Labs. Every tool performs zero-server processing — your health data never leaves your device.