Validation of the diagnosis of venous thromboembolism in general practice database studies

Aims The study was conducted to determine whether the method for selecting cases of venous thromboembolism (VTE) from general practice databases significantly affected the findings of an epidemiological study. Methods Cases of VTE were identified from the UK General Practice Research Database (GPRD) by searching for codes for deep vein thrombosis (DVT) and pulmonary embolism (PE). These had to be supported by evidence of anticoagulation and be exposed to a combined oral contraceptive (COC) at the time of the event. Additional information about the event was sought from general practitioners who were requested to complete a questionnaire and to supply anonymised copies of hospital letters and discharge summaries. Results Of the 285 cases identified from the GPRD, additional information was available for 177 VTE events. This information showed that 84% of those events were supported by hospital investigations or a death certificate. Using only verified cases, rather than all GPRD identified events, did not alter the results of the epidemiological study. Conclusions The GPRD provides information of sufficiently high quality to allow valid epidemiological research of VTE events. Excluding cases without a database record of hospital admission would lead to valid events being overlooked, and an under-estimate of the disease incidence.