Medical Data Standards and Terminologies
Two families to keep straight
Terminologies (vocabularies) describe meaning: SNOMED CT for clinical findings and procedures, LOINC for laboratory and clinical observations, ICD-10-CM for morbidity/billing diagnosis coding, RxNorm for medications, CPT/HCPCS for procedures and billing, and UMLS as a metathesaurus linking them. Messaging and exchange standards describe structure and transport: HL7 v2, HL7 FHIR, and previously CDA. Confusing a terminology with a messaging standard is the single most common error.
Concepts to master
- Code system vs. value set: a value set is a constrained subset of codes drawn from one or more code systems for a specific use.
- Mapping and crosswalks, including the difference between a one-to-one map and a broader/narrower semantic relationship.
- SNOMED CT's compositional grammar and concept model (is-a relationships, defining attributes).
- LOINC's six-axis structure (component, property, time, system, scale, method) and why axis errors cause mismatches.
- Local codes and the need for enterprise mapping to standard terminologies.
- ICD-10-CM specificity and laterality; the fact that ICD is not designed for clinical decision support granularity.
Traps
Questions may present a lab result and ask which standard governs its identity (LOINC) versus its transport (HL7/FHIR). Another trap is assuming a map is lossless-ICD to SNOMED mappings are frequently approximate. Also watch for value-set questions where the distractor is a whole code system rather than the constrained subset.
Worked example
A glucose result: LOINC identifies the observation (e.g., glucose in serum/plasma, mass concentration), FHIR carries it in an Observation resource, and SNOMED CT may code the specimen or finding context. Three different standards, three different jobs-name each role explicitly in your answer.