Venous thromboembolism discharge diagnoses in the Danish National Patient Registry should be used with caution

OBJECTIVE: We validated discharge diagnoses of venous thromboembolism (VTE) in the Danish National Patient Registry. STUDY DESIGN AND SETTING: We identified all first-time VTE discharge diagnoses in the Danish National Patient Registry among participants of the Danish cohort study "Diet, Cancer, and Health", in the period from 1994 to 2006. Medical records were retrieved and VTE diagnoses were verified by one of the authors using a standard protocol. The positive predictive value (PPV) of a discharge diagnosis of VTE was calculated as percent of registry diagnoses with the corresponding true diagnosis in the chart among all registry diagnoses. RESULTS: We retrieved medical records from 1,100 of 1,135 participants (96.9%) registered with a discharge diagnosis of VTE; 626 diagnoses were confirmed and 17 were considered probable. The PPV of diagnoses coded at wards was 75.0% (95% confidence interval: 71.9, 77.9). Diagnoses from emergency departments were not valid. The PPV varied by type of VTE (deep venous thrombosis and pulmonary embolism), type of diagnosis (primary or secondary), and sex. CONCLUSION: Data on VTE obtained from administrative registries are a valuable source of information but should be used with caution in medical research.