The coding of migration status in English primary care from 2011 to 2024: a pilot use of Open Code Counts

Background: The migration status of the 9.8 million migrants living in England is not systematically recorded in primary care electronic health records (EHRs). Codelist approaches enable us to create cohorts of individuals who have had a predefined, optional migration-related code (e.g. 'refugee') added to their EHR. Aims: We aimed to explore the use of migration-related SNOMED CT codes to inform future research using primary care data. Design and Setting: We used our Open Code Counts tool and R package to explore data published by NHS England on SNOMED CT code usage in English primary care. Method: We created migration-related codelists and described their use from 1st August 2011 to 31st July 2024. We compared code usage to trends in migration-related statistics from the Home Office and the 2021 Census. Results: There were 29.1 million uses of 1,114 migration-related codes from 2011 to 2024. Migration-related coding increased over time, exceeding the increase observed for coding overall, with a sharp increase from 2020, particularly for country-of-birth and language. Language coding represented 71% of code usage and where country of birth was recorded, there was mixed agreement with the census estimates. Coding of immigration legal statuses was low and overwhelmingly about asylum or refugee status. Conclusion: Rapid assessment of migration-related coding using Open Code Counts highlights that a non-English first language is the most strongly represented characteristic in migrant cohorts in English primary care EHRs, which should be considered when interpreting future research findings.