Objective: Thromboprophylaxis with a fixed dose of low-molecular-weight heparin is recommended for hospitalized acutely ill medical patients. The purpose of this study was to assess whether the anti-factor Xa (anti-Xa) activity of enoxaparin prescribed for venous thromboembolism prophylaxis depends on body mass index (BMI) in patients hospitalized for an acute respiratory disease.
Patients and methods: All patients admitted to the respiratory medicine department (January-December 2006) for an acute respiratory disease, and for whom pharmacologic thromboprophylaxis was indicated, were included in the study. Anti-Xa activity was measured 4 hours after administration of enoxaparin on the third day of hospitalization. The primary outcome was anti-Xa activity in relation to BMI.
Results: One hundred twelve patients were enrolled. Mean anti-Xa activity decreased with each BMI quartile (0.28, 0.23, 0.15, and 0.13 U/mL for quartiles 1, 2, 3, and 4, respectively). In the multivariate analysis, BMI was the only predictor of inadequate anti-Xa activity (odds ratio, 1.14; 95% confidence interval, 10.5-1.24; P< .002) after adjustment for age, sex, and serum creatinine levels. Two episodes of symptomatic proximal deep vein thrombosis were diagnosed in the month after hospitalization; both occurred in patients who had inadequate anti-Xa activity.
Conclusions: Anti-Xa activity is dependent on BMI in hospitalized acute medical patients receiving enoxaparin for thromboprophylaxis.