TerminologyStable

LOINC

Universal codes for labs, vitals, clinical observations, and surveys. Free, maintained by Regenstrief.

LOINC codes look like 8480-6 (Systolic BP) or 72514-3 (PHQ-9 total).

Used heavily in:

Observation.code (the dominant use case)

DiagnosticReport.code

Questionnaire.item.code (for standardized assessments like PHQ-9, AUDIT, etc.)

Pair with UCUM for units (mm[Hg], mg/dL).

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