Currently submitted to: Journal of Medical Internet Research
Date Submitted: Apr 16, 2026
Open Peer Review Period: Apr 17, 2026 - Jun 12, 2026
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Validation of a SNOMED CT-based ethnicity phenotype to support secondary uses of primary care computerised medical records: A cross-sectional study of 21 million patients in England
ABSTRACT
Background:
Large real-world data sources offer a unique opportunity to study the health of diverse ethnic groups. High-quality and accessible ethnicity data is needed to maximise this potential.
Objective:
To validate a newly developed ethnicity phenotype in the Oxford-Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC).
Methods:
Retrospective cross-sectional study of individuals registered at a practice within the Oxford-RCGP RSC on 4th December 2024. An updated ethnicity phenotype was implemented and validated. Ethnicity data quality was assessed by evaluating completeness, distribution, and accuracy through external validation against estimates from the 2021 UK Census.
Results:
Of 21,902,852 individuals, 88.63% (19,412,154) had a recorded ethnicity following the implementation of the updated ethnicity phenotype. There was a marked improvement in the recording of granular (19-point) ethnicity data, with completeness increasing from 69.06% (15,126,835) to 88.63% (19,412,154) with the updated phenotype. There was significant variation in the completeness of ethnicity data according to demographic subgroups. The proportion of individuals in each ethnicity group was within 3.56 percentage points of the 2021 Census estimates for the same ethnicity group across England. Larger relative differences were observed for non-White ethnic groups.
Conclusions:
The updated ethnicity phenotype provides high-quality and granular ethnicity data based on official classifications for almost 90% of individuals. The overall ethnicity breakdown in the Oxford-RCGP RSC population was broadly similar to 2021 UK Census estimates. The updated ethnicity phenotype supports secondary uses of primary care CMRs, providing high-quality and accessible ethnicity data to study the health of diverse ethnic groups.
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