Immunological studies on human antithrombin 3. Influence of age, sex and use of oral contraceptives on serum concentration.

Isolation of what is probably the main thrombin inhibitor antithrombin III (At-III) made the preparation of specific antisera for immunochemical analysis possible. When immunoelectrophoresis of At III against anti At III and anti whole human serum was performed a single precipitation arc was formed in the alpha 2-globulin region. When thrombin was added the apparent concentration of At III decreased. Serum concentration of At III is probably influenced by sex hormones since women of childbearing age have lower serum concentrations of At III. They are further decreased by oral contraceptive implying a relationship between the low At III levels and the tendency to thrombosis in women using oral contraceptives.