Monitoring anticoagulation therapy in patients with the lupus anticoagulant

Patients with a lupus anticoagulant (LAC) may present with thrombosis and a bnormal coagulation studies. It is important to recognize that these indivi duals may require special laboratory tests other than measuring the activat ed partial thromboplastin time or prothrombin time/international normalized ratio (PT/LNR) traditionally used by clinicians to monitor heparin and war farin. We recommend the use of a factor Xa inhibition test to regulate hepa rin in this patient population. This test measures the ability of heparin, as a cofactor of antithrombin III, to inhibit the catalytic function of fac tor Xa in plasma. Therapeutic levels are 0.3-0.7 U/mL of anti-Xa activity. For warfarin, we suggest measuring the factor X levels as determined by a c hromogenic assay, if the patient initially has a prolonged PT/INR. Therapeu tic levels are 10%-40% of normal values. In this article, we review this an d other tests available to monitor antithrombotic therapy in patients with the LAG.