Measurement of antithrombin(AT) activity in plasma provides important information for the diagnosis of congenital antithrombin deficiency and disseminated intravascular coagulation. When measured in the presence of heparin, plasma antithrombin activity includes heparin cofactor II activity as about 20-30% of the total activity. Antithrombin assay methods measuring plasma anti-F.Xa activity or those measured in the presence of 0.22M NaCl exclude the influence of HC II activity. Dilution of the plasma sample is necessary to measure the heparin cofactor anti-thrombin activity of AT correctly. A laboratory method that precisely reflects plasma heparin cofactor anti-thrombin activity of AT should be established as the standard laboratory method.

*Department of Laboratory Medicine, Kumamoto University School of Medicine, Kumamoto 860-0811

【Key Words】antithrombin, congenital antithrombin deficiency, disseminated intravascular coagulation, heparin cofactor II, factor Xa