Table 4 Summary of the main challenges involved in mapping registry data to the OMOP CDM, and their solutions

Mapping incomplete dates

Create standardized imputation rules to ‘restore’ missing dates

Mapping of MedDRA codes (classification concepts) to standard concepts

Automated mapping from the unified medical language system to the ICD-10, ICD-10-Clinical Modification or SNOMED vocabulary with crosslinks and name matching, followed by further expert review and additional manual mapping

Mapping of free text e.g. from medication tables

Free text extracted, custom mapped and contextualized via CONCEPT_RELATIONSHIP and CONCEPT_ANCESTOR tables

Mapping of non-existing OMOP vocabulary e.g. PH subgroups

Used either a combination of SNOMED concepts (e.g. PAH and underlying cause), or a new custom concept (e.g. drug- and toxin-induced PAH)

Mapping information that is related to another piece of information e.g. severity of an event

Separate clinical facts are stored in their appropriate domain and a link is added in the FACT_RELATIONSHIP table

Capturing the information that a procedure was not performed

This information was excluding from mapping, per the OMOP convention, but is planned for mapping in a future update