Bridging Gaps in Unified Clinical Terminology: The Necessity of Post-Coordination in SNOMED CT

We analyzed 23,595 SNOMED CT post-coordinated expressions from Geneva University Hospitals to evaluate their contribution to clinical coverage. Using a fine-tuned embedding model as a similarity measurement tool, we compared each post-coordination with concepts from 12 common terminologies, including SNOMED CT pre-coordinations. Nearly one quarter (24.3%) of post-coordinations aligned more closely with specialized terminologies such as LOINC and CPT, indicating that they capture information better represented elsewhere but not yet available in SNOMED CT. In addition, a substantial subset of post-coordinations showed low similarity to any existing vocabulary, reflecting highly specific institutional practices. These findings highlight post-coordination as essential for encoding fine-grained medical information within a unified terminology framework.