Reduced titers of Hageman factor (factor XII) in Orientals.

Hageman factor (factor XII) is a procoagulant upon which the surface-mediated generation of fibrinolytic activity and kinin formation depends. We found that the clotpromoting activity and antigenic properties of Hageman factor were present in lower levels in the plasma of a small group of Oriental subjects than in that of American whites, whereas the levels of plasma prekallikrein (Fletcher factor), high-molecular-weight kininogen (Fitzgerald factor), and plasma thromboplastin antecedent (factor XI) in plasma samples from Oriental subjects did not significantly differ from those from normal white subjects. In one family, there was an excess of plasma Hageman factor antigens with respect to functional activity. These findings stress the importance of defining the racial characteristics of subjects used to establish standards for clotting assays.