To assess the validity of venous thromboembolism (VTE) diagnoses registered in the Swedish National Patient Register (NPR) in patients with rheumatoid arthritis (RA).

We performed a validation study using manual chart reviews to validate ICD-10 codes for VTE from the NPR. We took a random sample of 269 VTE events registered at hospitals in Region Stockholm from 2009 to 2018 in patients with RA.

Medical records for all 269 VTE events were available for review. Overall, the positive predictive value (PPV) for a VTE diagnosis was 95%. For incident VTE events, the PPV was 87% and ranged from 80% to 98% across six more or less restricted alternative definitions of incident VTE event. Out of 235 confirmed incident VTE events, the vast majority were diagnosed independently of the RA disease (three cases occurred as a result of clinical work-up for a presumed RA-related sign or symptom, and in 17 cases did the work-up involve a rheumatologist).

This study demonstrates high validity for VTE diagnoses recorded in the NPR for patients with RA, thus confirming that the NPR may be used to identify prevalent VTE as well as incident VTE events in patients with RA. Our results further demonstrate that in patients with RA, diagnoses of VTE are only marginally influenced by work-up related to the rheumatic disease, suggesting a modest impact of surveillance or diagnostic bias.