A tentative classification of AT III congenital abnormalities.

Twenty two families with an abnormal antithrombin III have been described so far. A classification of these abnormality encounters many difficulties. In fact, the available classifications seem inadequate. On the basis of 5 tests, namely AT III progressive and/or global activity, heparin co-factor activities, crossed immunoelectrophoresis (CIE) without and with heparin, AT III antigen and heparin affinity studies, a "new" tentative classification is proposed. On the basis of these tests, AT III abnormalities may be subdivided in 5 groups: Group 1 includes asymptomatic patients with a variable defect in heparin cofactor activities with normal total or progressive AT III activity and with a slow peak in the heparin modified CIE. Group 2 comprises symptomatic patients with the same laboratory features as presented by group 1 patients. Group 3 includes families in which there is a variable reduction of all AT III activities. There is always a slow peak in the heparin modified CIE and patients are symptomatic. Group 4 includes patients with a variable decrease of all AT III activities but a normal CIE. Patients are symptomatic. Group 5 comprises symptomatic patients with variable decreased AT III activity, and with a fast moving peak in the plain (without heparin) CIE.