Mapping serves as a foundational pillar for achieving true semantic interoperability across diverse clinical systems. This mapping process primarily operates on two critical fronts:
- Internal codes to LOINC, the most common type of mapping activity
- LOINC to another ontology (or the reverse)
This page serves as a go-to destination for resources related to both types of mapping.
Overview of mapping with LOINC
This is a brief excerpt of an education day presentation given by Stan Huff at the 2025 LOINC Conference.
Local codes to LOINC
Regenstrief Institute has published a number of domain-specific guides for mapping concepts. You must be logged in using your free LOINC user ID and password to download these PDFs. This has been done so we may inform users of updates and potential errata. This work was supported by the U.S. Food and Drug Administration contract 75f40119c10140.
Download LOINC mapping guides
| Name | Published | Size |
|---|---|---|
| Allergy v1.0 | Sep 2022 | 1.94 MB |
| Cell Markers v1.0 | Sep 2022 | 2.71 MB |
| Chemistry v1.0 | Sep 2022 | 1.90 MB |
| Drug and Toxicology v1.0 | Sep 2022 | 1.67 MB |
| Hematology and Serology v1.0 | Sep 2022 | 1.77 MB |
| Microbiology v1.1 | Aug 2019 | 1.93 MB |
| Molecular Pathology v1.0 | Sep 2022 | 1.76 MB |
We welcome your feedback on these guides.
Mapping strategies
You may not necessarily need to map your entire catalog to LOINC. Regenstrief has culled a list of the Top 20,000 most frequently used LOINC codes. The top 10% (2,000 codes) of the rankings represent about 99% of total test volume.
These rankings are available in a number of locations including the Loinc.csv download file and LOINC Terminology Service in a field/property named COMMON_TEST_RANK. You can also see the rankings in SearchLOINC results in a column named Rank.
Mapping software
Regenstrief Institute makes available RELMA, a Windows application, to aid in mapping. It is updated with each LOINC release but otherwise remains in a maintenance mode. There are several commercial software products available to assist an organization with mapping.
LOINC to/from external ontologies
Regenstrief has mapped LOINC terms and LOINC Parts to several code systems. You can retrieve these relationships from the LOINC Complete file download. They are located in AccessoryFiles / PartFile / PartRelatedCodeMapping.csv. They include relationships to IEEE device codes, RadLex RPIDs and RIDS, RxNorm, PubChem, SNOMED CT, PhenX, and others.
Mappings are also available from the LOINC Terminology Service using HL7® FHIR®. The bidirectional maps exist within the ConceptMap resource.