Low molecular weight heparin for the prevention of deep venous thrombosis: a suitable monitoring in elderly patients?

Monitoring of anti-Xa activity (aXa) levels is not routinely required in patients receiving enoxaparine at prophylactic dosages, since aXa is supposed to stay below the manufacturer's recommended range in patients treated for venous thrombosis (0.5-1 IU/ml). In order to aXa in elderly subjects receiving prophylactic enoxaparin, 68 consecutive patients (mean age 82.5 +/- 10.7 years) hospitalized in a medical department receiving 4000 IU enoxaparin daily subcutaneously for the prevention of venous thromboembolic disease were studied. After the first injection of enoxaparin, the aXa of 57.4% patients was superior to 0.5 IU/ml while 69.4% had an aXa higher than 0.5 after 8.4 +/- 1.2 days. A negative relationship between aXa and body weight and a trend towards a positive correlation between aXa and age but not with creatinine clearance were noted. Our findings question the opportunity to monitor aXa in elderly patients receiving 4000 IU enoxaparin as antithrombotic prophylaxis.