Observation resource group

An Observation resource records one measurement or one finding about the patient. Observations hold what the clinician measured or saw. The interpretation, such as a diagnosis, goes into a Condition. The resource follows the FHIR R4 Observation specification, and each field name below links to its R4 definition.

If you already receive lab results or vital signs as structured data, use that source and turn off the laboratory and vital-signs categories. A value copied into a note can be wrong or out of date. See Reduce extraction errors.

One Observation per value

Each number or finding gets its own Observation. A blood pressure of “150/90” becomes two Observations, one systolic and one diastolic. A panel such as “Na 139, K 4.1” becomes one Observation per analyte. The endpoint does not use the FHIR component field.

Measurements and findings

Every Observation is one of two kinds. The kind decides which coding system code uses, and where the result goes.

	Measurement	Finding
What it is	A value that someone measured or scored	Something that someone saw, heard, or felt
Note says	”HbA1c 7.2 %”, “Heart rate 88”, “PHQ-9 score 14"	"No murmurs”, “Abdominal tenderness”, “Never smoked”
`code`	What the clinician measured, in LOINC: `4548-4` Hemoglobin A1c	The finding itself, in SNOMED CT: `88610006` Heart murmur
Result	A number in `valueQuantity` (with a unit), `valueInteger`, or `valueRatio`	A SNOMED CT qualifier in `valueCodeableConcept`, such as Present or Absent

Read it as a question and an answer. For a measurement, code asks “what is the HbA1c?” and the value answers “7.2 %”. For a finding, code names the finding, “heart murmur”, and the value says whether the clinician found it: “absent”.

Same topic, different kinds

A single topic can produce both kinds. The wording in the note decides:

Note says	Kind	`code`	Result
”20 pack-years”	Measurement	LOINC term for tobacco pack-years	`valueQuantity`: 20
”Never smoked”	Finding	SNOMED CT finding for tobacco smoking	`valueCodeableConcept`: Absent
”Ejection fraction 55 % on echo”	Measurement	LOINC term for left ventricular ejection fraction	`valueQuantity`: 55 %
“No pericardial effusion on echo”	Finding	`373945007` Pericardial effusion	`valueCodeableConcept`: `2667000` Absent
”Severe stenosis at L4-L5 on MRI”	Finding	SNOMED CT finding for spinal stenosis	`valueCodeableConcept`: Severe, with `bodySite` L4-L5

When you read an Observation, check the value field before you use code. A finding Observation with the value Absent means the patient does not have that finding. Code 88610006 Heart murmur on its own does not mean the patient has a murmur.

A finding names the finding in positive form, with presence or absence in the value. “No acute hemorrhage” becomes the code for intracranial hemorrhage, with the value Absent, not a code meaning “no hemorrhage”.

Normal and absent findings

Findings let you record what the clinician did not find. A list of codes has no way to say “no murmur”. An Observation does:

Note says	`code`	`valueCodeableConcept`
”Murmur heard at apex”	`88610006` Heart murmur	`52101004` Present
”No murmurs”	`88610006` Heart murmur	`2667000` Absent

Category	Example from a note	Kind	`code`
`vital-signs`	”BP 150/90”, “HR 88”, “Temp 38.2”	Measurement	LOINC
`laboratory`	”HbA1c 7.2 %”, “Potassium 4.1 mmol/L”	Measurement	LOINC
`survey`	”PHQ-9 score 14”, “GCS 15”	Measurement	LOINC
`exam`	”No murmurs”, “Abdominal tenderness”	Finding	SNOMED CT
`social-history`	”20 pack-years”, “Never smoked”	Both	LOINC for measurements, SNOMED CT for findings
`imaging`	”Ejection fraction 55 %”, “Chest X-ray shows consolidation”	Both	LOINC for measurements, SNOMED CT for findings
`procedure`	”QTc 450 ms”, “ECG shows sinus rhythm”	Both	LOINC for measurements, SNOMED CT for findings

Fields

Field	Type	What it holds	Example from a note
`status`	code	`final` by default. Also `registered`, `preliminary`, `amended`, `corrected`, `cancelled`, `entered-in-error`, or `unknown`. See the R4 value set.	”preliminary result” → `preliminary`
`category`	CodeableConcept list	One of the seven categories above. See the R4 value set.
`code`	CodeableConcept	What the clinician measured or found, in LOINC or SNOMED CT	”HbA1c” → `4548-4`
`valueQuantity`	Quantity	A number with a unit (`value`, `unit`, `comparator`, `system`)	“HbA1c 7.2 %” → `7.2`, `%`
`valueInteger`	integer	A whole-number score	”GCS 15” → `15`
`valueRatio`	Ratio	A ratio (`numerator`, `denominator`)	“titer 1:64”
`valueCodeableConcept`	CodeableConcept	The result of a finding, as a SNOMED CT qualifier such as Present, Absent, or Severe	”no murmurs” → Absent
`interpretation`	CodeableConcept list	One of nine HL7 interpretation codes: `N` Normal, `A` Abnormal, `H` High, `L` Low, `HH` Critical high, `LL` Critical low, `POS` Positive, `NEG` Negative, or `ND` Not detected. `laboratory` uses all nine, `vital-signs` only `N`, `H`, and `L`, `imaging` and `procedure` only `N`, `A`, `H`, and `L`, and `survey` only `N` and `A`. `exam` and `social-history` Observations have no interpretation. See the R4 value set.	”potassium low at 3.1” → `L`
`bodySite`	CodeableConcept	Where on the body, in SNOMED CT	”BP right arm” → right upper arm structure
`effectiveDateTime`	dateTime	When the measurement was taken. Only when the note states a date. A time of day without a timezone is cut back to the date, because R4 accepts a time only with a timezone offset.	”HbA1c 7.2 % on 2026-10-12” → `2026-10-12`
`note`	list of Annotation	Extra context
`subject`	Reference	The Patient of the Bundle
`encounter`	Reference	The Encounter of the note
`extension`	list of Extension	Mentions and alternatives

Units

A unit comes from the note, or from a fixed default for a few common measurements. For example, a heart rate written without a unit gets beats/min, and a temperature of 37.2 gets °C. The endpoint does not guess an ambiguous unit: “weight 180” keeps no unit. Every unit uses system: "http://unitsofmeasure.org" (UCUM). The unit is the text as the note writes it, and the Quantity carries no UCUM code.

Codes the endpoint can assign

The endpoint only searches a fixed part of each coding system for each field. A code outside that part never appears, and a filter can only narrow the part further, never widen it. Codes come from a fixed scope explains why. The allowed codes depend on the category, and on whether the Observation is a measurement or a finding:

Category	`code` for measurements	`code` for findings	`valueCodeableConcept`	`bodySite`
`laboratory`	LOINC, status `ACTIVE`			none
`vital-signs`	LOINC, status `ACTIVE`			Body structure
`survey`	LOINC, status `ACTIVE`			Body structure
`exam`		Clinical finding	Present or Absent	Body structure
`social-history`	LOINC, status `ACTIVE`	Clinical finding	Present or Absent	Body structure
`procedure`	LOINC, status `ACTIVE`	Clinical finding	Present or Absent	Body structure
`imaging`	LOINC, status `ACTIVE`	Clinical finding	Semantic tag `qualifier value`	Body structure

What the short names mean:

Name	Allowed codes
LOINC, status `ACTIVE`	Any LOINC term with status `ACTIVE`. The endpoint never returns `TRIAL`, `DISCOURAGED`, or `DEPRECATED` terms.
Clinical finding	SNOMED CT `404684003` Clinical finding, and its descendants. This includes disorders, such as `373945007` Pericardial effusion.
Present or Absent	A fixed pair: SNOMED CT `52101004` Present and `2667000` Absent
Semantic tag `qualifier value`	Any SNOMED CT qualifier value, such as `52101004` Present, `24484000` Severe, or a word that describes size or shape
Body structure	SNOMED CT `442083009` Anatomical or acquired body structure, and its descendants

category, status, and interpretation use the fixed HL7 value sets listed under Fields.

Examples

Lab result

HbA1c 7.2 % on 2026-10-12, up from 6.8 %.

Simplified
JSON

Field	Value
`category`	`laboratory`
`code`	`4548-4` Hemoglobin A1c/Hemoglobin.total in Blood (LOINC)
`valueQuantity`	7.2 %
`effectiveDateTime`	`2026-10-12`

{
  "resourceType": "Observation",
  "id": "8f0c6b8e-3d5a-5b7e-9a41-2c6d0e7f1a93",
  "status": "final",
  "category": [
    {
      "coding": [
        {
          "system": "http://terminology.hl7.org/CodeSystem/observation-category",
          "code": "laboratory",
          "display": "Laboratory"
        }
      ],
      "text": "Laboratory"
    }
  ],
  "code": {
    "coding": [
      {
        "system": "http://loinc.org",
        "code": "4548-4",
        "display": "Hemoglobin A1c/Hemoglobin.total in Blood"
      }
    ],
    "text": "Hemoglobin A1c/Hemoglobin.total in Blood"
  },
  "subject": { "reference": "urn:uuid:b49ecda5-92db-5325-a7a9-f82c71500bad", "type": "Patient" },
  "encounter": {
    "reference": "urn:uuid:29543af8-9ec2-528e-8a3b-1e891822d99d",
    "type": "Encounter",
    "identifier": {
      "system": "http://corti.app/fhir/identifier/encounter",
      "value": "enc-88213"
    }
  },
  "effectiveDateTime": "2026-10-12",
  "valueQuantity": {
    "value": 7.2,
    "unit": "%",
    "system": "http://unitsofmeasure.org"
  }
}

The earlier value of 6.8 % gets its own laboratory Observation. It has no effectiveDateTime, because the note does not say when the lab measured it.

Exam finding

Heart: regular rhythm, no murmurs.

Simplified
JSON

Field	Value
`category`	`exam`
`code`	`88610006` Heart murmur
`valueCodeableConcept`	`2667000` Absent

{
  "resourceType": "Observation",
  "id": "c47e2a19-6b0d-5f83-8e25-9d1a3b4c5e60",
  "status": "final",
  "category": [
    {
      "coding": [
        {
          "system": "http://terminology.hl7.org/CodeSystem/observation-category",
          "code": "exam",
          "display": "Exam"
        }
      ],
      "text": "Exam"
    }
  ],
  "code": {
    "coding": [
      {
        "system": "http://snomed.info/sct",
        "code": "88610006",
        "display": "Heart murmur"
      }
    ],
    "text": "Heart murmur"
  },
  "subject": { "reference": "urn:uuid:b49ecda5-92db-5325-a7a9-f82c71500bad", "type": "Patient" },
  "encounter": {
    "reference": "urn:uuid:29543af8-9ec2-528e-8a3b-1e891822d99d",
    "type": "Encounter",
    "identifier": {
      "system": "http://corti.app/fhir/identifier/encounter",
      "value": "enc-88213"
    }
  },
  "valueCodeableConcept": {
    "coding": [
      {
        "system": "http://snomed.info/sct",
        "code": "2667000",
        "display": "Absent"
      }
    ],
    "text": "Absent"
  }
}

“Regular rhythm” is a separate finding, so it gets its own exam Observation. For a vital-sign example with two Observations for one blood pressure, see the full response in Extract FHIR resources.

Clinical Text Generation

Medical Coding

FHIR Extraction

Clinical Assistant

One Observation per value

Measurements and findings

Same topic, different kinds

Normal and absent findings

Categories

Fields

Units

Codes the endpoint can assign

Examples

Lab result

Exam finding

Next steps

Procedure resource group

Filter FHIR resources

​One Observation per value

​Measurements and findings

​Same topic, different kinds

​Normal and absent findings

​Categories

​Fields

​Units

​Codes the endpoint can assign

​Examples

​Lab result

​Exam finding

​Next steps

Procedure resource group

Filter FHIR resources

One Observation per value

Measurements and findings

Same topic, different kinds

Normal and absent findings

Categories

Fields

Units

Codes the endpoint can assign

Examples

Lab result

Exam finding

Next steps