In Europe, the diversity of medical coding systems used in electronic health data creates significant challenges in defining and retrieving study variables consistently across datasets. A concept defined in one coding system cannot be directly applied in another without harmonisation. The VAC4EU Code List tackles this issue by offering a centralised, semi-automated platform built on the CodeMapper system for creating harmonised, multilingual, and version-controlled codelists. These codelists serve as reusable, metadata-rich reference standards that can be tailored and reused in future studies, promoting consistency and transparency across projects.
Originally developed during the ADVANCE project, the tool has been further refined within VAC4EU to support federated studies and regulatory decision-making. The VAC4EU Code List Taskforce actively manages this resource by defining target concepts, initiating mapping, involving medical experts for review, and supporting ongoing updates to integrate new vocabularies and code system versions. Recent advancements include the ability to incorporate non-UMLS vocabularies, assign editor roles, track version history, and display cross-project use of existing codelists enhancing transparency and reusability across studies.