OMOP CDM — Observational Medical Outcomes Partnership Common Data Model
Overview
The OMOP Common Data Model (CDM) is the open standard for structuring observational health data, including EHR records, insurance claims, and registries, into a common format that enables federated analytical studies across institutions without sharing raw patient data. It was developed within the OMOP initiative, a public-private partnership involving the FDA, academic institutions, and pharmaceutical companies, and is now maintained by OHDSI. It supports federated distributed network studies in which each site runs the same analytical code locally and shares only aggregate results. The EHDS recommends OMOP CDM as the common data format for secondary use across EU Member States.
Interoperability
OMOP CDM and HL7 FHIR interoperability is being developed through a joint initiative between OHDSI and the HL7 Vulcan Accelerator, with a FHIR-to-OMOP transformation specification under active development as of 2025. OMOP-to-FHIR tooling exists but a fully standardised bidirectional mapping is not yet complete. OMOP CDM also maps to CDISC SDTM for clinical trial data integration, with conversion guidance maintained by the OHDSI Clinical Trials Working Group.
CDM Structure
The OMOP CDM organises clinical data into domain tables. Each domain maps source codes to a standard vocabulary: conditions to SNOMED CT, drugs to RxNorm, procedures to SNOMED CT and CCAM, and measurements to LOINC. Source codes from ICD-10, MedDRA, and local systems are mapped to OMOP standard concepts via Athena, which also covers ICD-11, MeSH, HPO, MONDO, ORDO, and NDC.
| Domain | Table | Contents |
|---|---|---|
| Person | PERSON | Demographics, one row per patient |
| Observation Period | OBSERVATION_PERIOD | Periods of clinical data availability |
| Visit | VISIT_OCCURRENCE | Hospital stays, outpatient visits, ED |
| Condition | CONDITION_OCCURRENCE | Diagnoses (coded to SNOMED CT) |
| Drug | DRUG_EXPOSURE | Prescriptions and administrations (coded to RxNorm) |
| Procedure | PROCEDURE_OCCURRENCE | Clinical procedures (coded to SNOMED CT, CCAM) |
| Measurement | MEASUREMENT | Lab results and vitals (coded to LOINC) |
| Observation | OBSERVATION | Clinical findings not fitting other domains |
| Note | NOTE | Unstructured clinical notes |
| Death | DEATH | Date and cause of death |
| Specimen | SPECIMEN | Biological samples |
Connections
- Maintained by: OHDSI
- Recommended by: EHDS (OMOP CDM recommended for secondary use across EU Member States)
- Vocabularies: SNOMED CT, LOINC, ICD-10, ICD-11, MedDRA, CCAM, RxNorm, MeSH, HPO, MONDO, ORDO
Resources
- https://hl7vulcan.org/projects/fhir-to-omop/ (HL7 Vulcan FHIR-to-OMOP project)
- https://ohdsi.org
- https://ohdsi.github.io/CommonDataModel/ (CDM specification)
- https://github.com/OHDSI/CommonDataModel (GitHub)
- https://athena.ohdsi.org (OMOP vocabulary browser and download)
- https://doi.org/10.1093/jamia/ocad247 (Reich et al. 2024, JAMIA, OHDSI vocabularies)