Validation of risk assessment models for venous thrombosis in hospitalized medical patients

Background: Risk assessment models (RAMs) have been developed to predict which medical patients are at high risk for venous thrombosis (VT) and hence, should receive pharmacological thromboprophylaxis. Possibly due to the limited performance of the current models, guidelines differ on thromboprophylaxis regimens. Objective: In this study all known RAMS were externally validated in medical patients in order to guide physicians in their thromboprophylaxis strategies. Patients and Methods: A literature search was performed to find all published RAMs for medical patients at risk for VT. Data from a large population based case-control study (MEGA study) designed to identify risk factors for a first VT were used to externally validate each RAM. Results: 516 patients and 40 controls met the inclusion criteria for being a medical patient out of 4956 cases and 6297 controls). The c-statistic, sensitivity, specificity, negative, and positive predictive values were calculated for each RAM. The literature search yielded 12 RAMs, none of which showed good discrimination (area under the curve range 0.56-0.66), high sensitivity or specificity. The negative predictive value was high in all the RAMs (range 98.6-99.4) and positive predictive value was low (range 1.1-3.4). Conclusion: This study shows that the discriminative power of currently available RAMs to predict VT in medical patients is limited. Therefore, clinical judgment should supplement RAMs to identify high-risk medical patients for thromboprophylaxis. These results underline the importance of improving the performance of these models.