Monitoring anticoagulant effect of low molecular weight heparin

The anticoagulant effect of low molecular weight heparin (LMWH) (eg enoxaparin, dalteparin) is usually predictable, so routine anticoagulation monitoring using anti-Xa levels is not required.

Anti-Xa levels are not monitored for patients using LMWH for primary VTE prophylaxis.

For patients receiving therapeutic LMWH, a specialist may consider anticoagulation monitoring using anti-Xa levels if there is:

• impaired kidney function
• active bleeding or thrombosis during long-term therapy
• low body weight (less than 50 kg)
• obesity (weight more than 150 kg or body mass index [BMI] more than 40 kg/m²)
• pregnancy.

Use local laboratory ranges because therapeutic anti-Xa ranges differ between laboratories. For patients with normal kidney function receiving therapeutic doses of LMWH, the target range of anti-Xa levels for the once-daily dosage regimen is different to the target range for the twice-daily dosage regimen.