LOINC (Logical Observation Identifiers Names and Codes) is the global standard for identifying laboratory and clinical observations. In labs, LOINC uniquely labels the test that was ordered/resulted so systems can exchange and interpret results consistently.
Why LOINC matters
- Interoperability: Ensures EHRs, HIEs, public health, and payers understand the same test across systems and vendors.
- Clinical decision support and analytics: Enables apples-to-apples aggregation, quality measures, and population health reporting.
- Public health/reporting: Required or strongly preferred for ELR, syndromic surveillance, and registries.
- Vendor/instrument neutrality: Decouples local test names from shared meaning.
Where LOINC is used in lab workflows
- Test catalog and LIS mapping: Each orderable and each resulted analyte maps to a LOINC.
Interfaces/messaging:
- HL7 v2:
OBX-3 (observation identifier) and often OBR-4 (order code) carry LOINC (with local codes as alternates). - FHIR:
Observation.code (and Observation.component.code) use LOINC; ServiceRequest.code for orders.
- Panels and components: Use a panel LOINC for the order plus individual LOINCs for each reported analyte.
- Units: Pair with UCUM units for machine-readable quantities.
How LOINC defines a test
LOINC names are built from six key attributes:
- Component (what is measured)
- Property (e.g., substance concentration, mass concentration)
- Time (e.g., point-in-time vs. 24-hour)
- System (specimen, e.g., serum/plasma, urine)
- Scale (quantitative, ordinal, nominal)
- Method (only when clinically relevant)
Prefer methodless codes unless the method changes clinical meaning or policy.
Practical examples
- 2160-0: Creatinine [Mass/volume] in Serum or Plasma
- 2951-2: Sodium [Moles/volume] in Serum or Plasma
- 4548-4: Hemoglobin A1c/Hemoglobin.total in Blood
- 718-7: Hemoglobin [Mass/volume] in Blood
Best practices for labs
- Maintain a governed LOINC mapping table in the LIS with effective dates and versioning.
- Map both orderables (panels) and each resulted analyte; don’t send generic panel codes for individual results.
- Use UCUM units that match the LOINC property (e.g., mmol/L for substance concentration).
- Revalidate mappings when methods, specimen types, or reportable elements change.
- Keep up with LOINC releases (biannual) and update mappings accordingly.
- Document rationale for method-specific mappings and avoid over‑specific codes when not needed.
Common pitfalls
- Using method-specific LOINCs when method doesn’t matter (reduces comparability).
- Sending a single panel LOINC for all component OBXs (loses analyte-level semantics).
- Mismatched units/property (e.g., mg/dL with a substance-concentration LOINC expecting mmol/L).
- Not remapping after instrument/methodology changes.
How LOINC relates to other code sets
- CPT/HCPCS: For billing/reimbursement; LOINC is not for billing.
- ICD‑10‑CM: Diagnoses justify medical necessity; independent of LOINC.
- SNOMED CT: Often used for result values (answers) and organisms, while LOINC represents the question (test).
Bottom line: LOINC is the backbone of semantic interoperability for lab data—map it carefully, pair it with UCUM units, keep it current, and use analyte-level codes for meaningful, computable results.