LOINC code mapping for biomarkers

[elkimek]

Summary

Add optional LOINC (Logical Observation Identifiers Names and Codes) codes as metadata on biomarkers. LOINC is the universal standard for identifying lab tests — like ISBN for books but for biomarkers. 71,000+ codes maintained by the Regenstrief Institute (nonprofit, free to use).

Suggested by @fpietrosanti in #57.

Why

• FHIR import: Pull lab results from Apple Health, Epic MyChart, or any EHR that exports FHIR — tests are identified by LOINC codes
• FHIR export: A getbased export with LOINC codes could be imported by other health tools
• Interoperability: Standard way to identify tests across systems, languages, and labs
• AI parsing: Could use LOINC as an additional signal for unambiguous marker identification

Implementation

1. Add optional loinc field to MARKER_SCHEMA entries (e.g., { key: 'glucose', loinc: '2345-7', ... })
2. Build a lookup table mapping ~200 existing category.markerKey → LOINC codes
3. Include LOINC codes in JSON export
4. Future: FHIR R4 Observation import/export module

Examples

Marker	Key	LOINC
Glucose	biochemistry.glucose	2345-7
Hemoglobin	hematology.hemoglobin	718-7
Total Cholesterol	lipids.totalCholesterol	2093-3
Testosterone	hormones.testosterone	2986-8
TSH	thyroid.tsh	3016-3

Notes

• Non-breaking: loinc field is optional, doesn't affect existing functionality
• Specialty labs (OAT, fatty acids) may not have LOINC codes — custom markers stay as-is
• Main effort is the mapping work (~200 standard markers)
• LOINC is free to use but the full database requires a free license from loinc.org

References

• https://loinc.org
• https://en.wikipedia.org/wiki/LOINC
• HL7 FHIR Observation: https://www.hl7.org/fhir/observation.html