Identification of residual risk factors for the development of venous thromboembolism in medical inpatients receiving subcutaneous heparin therapy for prophylaxis

OBJECTIVES: Venous thromboembolism (VTE) such as pulmonary embolism and deep venous thrombosis is the most common cause of preventable morbidity and mortality in hospitalized patients. Prophylaxis is recommended for medical patients older than 40 years with at least one risk factor. However, the currently recommended regimen prevents only about half of in-hospital VTE. The aim of this study was to identify the risk factors for development of VTE in medical inpatients who were already on recommended pharmacological prophylaxis. METHODS: We performed a retrospective cohort study of 10 633 patients who were admitted to the medicine service and received prophylaxis with subcutaneous unfractionated heparin. The diagnoses of pulmonary embolism and deep venous thrombosis were confirmed with computed tomography angiography and Doppler ultrasound, respectively. Univariate analysis with the χ-test, followed by log-linear Poisson regression analysis was performed to determine the relative risk associated with each factor. RESULTS: Sixty cases of in-hospital VTE [raw incidence, 0.6%; 95% confidence interval (0.43-0.72)] were observed. On univariate analysis, a previous history of VTE or an active malignancy were found to be significant residual risk factors for the development of in-hospital VTE. On multivariate analysis, only a previous history of VTE remained a significant independent risk factor [relative risk=30.1; 95% confidence interval (17.1-53.0); P<0.0001]. CONCLUSION: Among hospitalized patients admitted to the medicine service and receiving VTE prophylaxis with subcutaneous unfractionated heparin, those with a previous history of VTE were at a significant risk of developing in-hospital VTE. This at-risk population should be considered for more aggressive therapy to prevent recurrent VTE.