External Validation of the Padua and IMPROVE-VTE Risk Assessment Models for Predicting Venous Thromboembolism in Hospitalized Adult Medical Patients: A Retrospective Single-Center Study in Japan

Objectives: To assess the external validity of the Padua and International Medical Prevention Registry on Venous Thromboembolism (IMPROVE-VTE) risk assessment models (RAMs) for predicting venous thromboembolism (VTE) within 90 days of admission among hospitalized medical patients in Japan. Materials and Methods: A university hospital cohort comprising 3876 consecutive patients ages ≥15 years admitted to a general internal medicine department between July 2016 and July 2021 was retrospectively analyzed using data extracted from their medical records. Results: A total of 74 VTE events (1.9%), including six cases with pulmonary embolism (0.2%), were observed. Both RAMs had poor discriminative performance (C-index=0.64 for both) and generally underestimated VTE risks. However, recalibrating the IMPROVE-VTE RAM to update the baseline hazard improved the calibration (calibration slope=1.01). Decision curve analysis showed that a management strategy with no prediction model outperformed a clinical management strategy guided by the originally proposed RAMs. Conclusions: Both RAMs require an update to function in this particular setting. Further studies with a larger-sized cohort, including re-estimation of the individual regression coefficients with additional, more context-specific predictors, are needed to create a useful model that would help advance risk-oriented VTE prevention programs.