Laboratory diagnosis of antithrombin and heparin cofactor II deficiency

Antithrombin activity should probably be determined in persons with early onset of recurrent thrombosis, especially if a family history is present. The initial screening test should be a heparin cofactor assay optimized to reduce the contribution of heparin cofactor II. If the heparin cofactor assay is low, an antigenic determination should be performed to rule out the possibility of an antithrombin variant. At the present time, there is insufficient evidence to recommend the routine determination of heparin cofactor II levels in patients with thrombosis.