Recent Developments in Clinical Terminologies - SNOMED CT, LOINC, and RxNorm

Abstract

Objective: To discuss recent developments in clinical terminologies. SNOMED CT (Systematized Nomenclature of Medicine Clinical Terms) is the world's largest clinical terminology, developed by an international consortium. LOINC (Logical Observation Identifiers, Names, and Codes) is an international terminology widely used for clinical and laboratory observations. RxNorm is the standard drug terminology in the U.S.

Methods and results: We present a brief review of the history, current state, and future development of SNOMED CT, LOINC and RxNorm. We also analyze their similarities and differences, and outline areas for greater interoperability among them.

Conclusions: With different starting points, representation formalisms, funding sources, and evolutionary paths, SNOMED CT, LOINC, and RxNorm have evolved over the past few decades into three major clinical terminologies supporting key use cases in clinical practice. Despite their differences, partnerships have been created among their development teams to facilitate interoperability and minimize duplication of effort.

Fig. 1

Evolution of the number of concepts, relationships, and English descriptions in SNOMED CT over time.

Fig. 2

Evolution of the number of LOINC terms (all terms, and laboratory terms only) over time.

Fig. 3

Organizational structure of RxNorm, with its different types of drug entities (ingredient, brand name, clinical drug component, branded drug component, clinical drug, branded drug, generic pack, branded pack), using Azithromycin products as an example. Generic entities are on the left-hand side and branded entities are on the right hand-side. The definitional elements for each type of drug entity are indicated on the left. The lines between types of drug entities represent named relationships in RxNorm. (Relationship names are omitted for simplicity).

Fig. 4

Evolution of the number of active RxNorm concepts over time.