Correlation of plasma coagulation parameters with thromboprophylaxis, patient characteristics, and outcome in the MEDENOX study.

CONTEXT: Plasma anti-Xa and anti-IIa activities correlate with the dose of low-molecular-weight heparin, and D-dimer and thrombin-antithrombin complexes are markers of procoagulant activity. OBJECTIVE: To investigate the relationship between plasma coagulation parameters and patient characteristics, including renal function, thromboprophylaxis, and incidence of venous thromboembolism (VTE) in the MEDENOX study population. DESIGN: Controlled, multicenter, double-blind, randomized study. PATIENTS: Two hundred twenty-four acutely ill medical patients. INTERVENTIONS: Either 20 or 40 mg of enoxaparin administered subcutaneously or a placebo once daily for 10 (+/-4) days. MAIN OUTCOME MEASURES: VTE and plasma anti-Xa and anti-IIa activities, D-dimer, and thrombin-antithrombin levels in blood collected before prophylaxis was given (day 0) and after the last injection of the study drug. RESULTS AND CONCLUSIONS: Anti-Xa activity correlated with the dose of enoxaparin. In patients with mild or moderate renal impairment, there was no significant relationship between anti-Xa activity and the creatinine clearance rate. D-dimer concentrations were lower at day 10 (+/-4) in the 40-mg group, which had a 63% lower VTE incidence, than at day 0. No venographically confirmed thromboses were found in patients with a normal D-dimer concentration (<0.5 microg/mL [0.5 mg/L]). D-dimer levels were higher in patients with VTE than in those without VTE, but no predictive value could be demonstrated for individual patients.