Heparin monitoring in acute thrombosis associated with antiphospholipid antibody syndrome.

Antiphospholipid antibody syndrome is associated with recurrent thromboembolism and the presence of antibodies directed against negatively charged phospholipids. Despite significant hypercoagulability, patients with the disorder often have elevated baseline activated partial thromboplastin times. Although heparin is indicated for the treatment of acute thrombosis, heparin monitoring is complicated by laboratory test interference. A practical treatment approach involves patient-specific screening for a reagent insensitive to the presence of the inhibitor, and determination of a reagent-specific therapeutic range in seconds that corresponds to heparin serum concentrations of 0.2-0.4 U/ml. Other monitoring methods, including using the patient's baseline activated partial thromboplastin time or using an antifactor Xa activity assay, have not been reported or studied but may offer alternatives for heparin monitoring in patients with coagulation laboratory test interference associated with antiphospholipid antibody syndrome.