Quality of venous thromboembolism diagnoses among prostate cancer patients in the Danish National Registry of Patients

Aska Drljevic,1 Michael Borre,2 Morten Høyer,3 Vera Ehrenstein,4 Mary Nguyen-Nielsen4 1Department of Pharmacology, 2Department of Urology, 3Department of Oncology, 4Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark Background and aim: It is well established that cancer patients have an increased risk of venous thromboembolism (VTE). However, no previous study has examined the quality of VTE diagnoses related to cancer patients in the Danish National Registry of Patients (DNRP). To support future studies on cancer and risk of VTE, this study aimed to estimate the positive predictive value (PPV) of VTE diagnoses among prostate cancer (PC) patients registered in the DNRP. Materials and methods: We conducted a validation study using data from hospitals within the Central Denmark Region, which covers a population of 1.3 million people. Using the DNRP, we identified a total of 120 PC patients registered with VTE within the period 1995–2012. We also identified a random sample of 120 PC patients with no VTE registration within the same period. Therefore, a total of 240 patients were selected for medical chart review. We compared data from the DNRP to data collected from medical record review (ie, reference standard). We then computed PPV, sensitivity, and specificity with corresponding 95% confidence intervals (CIs) using the Jeffreys method. Results: The final study sample included 232 PC patients, of which 115 were registered with VTE and 117 had no registration of VTE in the DNRP. We found the overall PPV of VTE diagnoses in the DNRP to be 86.1% (95% CI 78.9%–91.5%). Sensitivity was 98.0% (95% CI 93.8%–99.6%), and specificity was 87.8% (95% CI 81.4%–92.6%). We also found the PPV of incident PC diagnoses in the DNRP to be 98.3% (95% CI 96.1%–99.4%). Conclusion: For PC patients, the registration of VTE diagnoses in the DNRP is associated with a high PPV. We provide evidence that data from the DNRP are valid for studies on risk of VTE among cancer patients. Keywords: positive predictive value, prostatic neoplasms, validation study, venous thromboembolis