A decision model to estimate a risk threshold for venous thromboembolism prophylaxis in hospitalized medical patients

Background: Venous thromboembolism (VTE) is a common preventable condition in medical inpatients. Thromboprophylaxis is recommended for inpatients who are not at low risk of VTE, but no specific risk threshold for prophylaxis has been defined. Objective: To determine a threshold for prophylaxis based on risk of VTE. Patients/ Methods: We constructed a decision model with a decision-tree following patients for 3 months after hospitalization, and a lifetime Markov model with 3-month cycles. The model tracked symptomatic deep vein thromboses and pulmonary emboli, bleeding events and heparin- induced thrombocytopenia. Long-term complications included recurrent VTE, post-thrombotic syndrome and pulmonary hypertension. For the base case, we considered medical inpatients aged 66 years, having a life expectancy of 13.5 years, VTE risk of 1.4% and bleeding risk of 2.7%. Patients received enoxaparin 40 mg day(-1) for prophylaxis. Results: Assuming a willingness-to-pay (WTP) threshold of $ 100 000/quality-adjusted life year QALY), prophylaxis was indicated for an average medical inpatient with a VTE risk of = 1.0% up to 3 months after hospitalization. For the average patient, prophylaxis was not indicated when the bleeding risk was > 8.1%, the patient's age was > 73.4 years or the cost of enoxaparin exceeded $ 60/dose. If VTE risk was < 0.26% or bleeding risk was > 19%, the risks of prophylaxis outweighed benefits. The prophylaxis threshold was relatively insensitive to low-molecular-weight heparin cost and bleeding risk, but very sensitive to patient age and life expectancy. Conclusions: The decision to offer prophylaxis should be personalized based on patient VTE risk, age and life expectancy. At a WTP of $ 100 000/QALY, prophylaxis is not warranted for most patients with a 3-month VTE risk below 1.0%.