The Assay of a Plasma Component Necessary for the Generation of a Plasminogen Activator in the Presence of Hageman Factor (Hageman Factor Co‐factor)

S ummary . Kaolin‐induced generation of fibrinolytic activity requires, in addition to factor XII (Hageman factor) and plasminogen, at least one further plasma factor which has been termed Hageman factor co‐factor (HF co‐factor). A technique for the assay of HF co‐factor in plasma is described using plasma specifically depleted of HF co‐factor by treatment with glass. The kaolin‐induced lysis time bears log:log relationship to the concentration of untreated test plasma diluted glass‐adsorbed plasma. The influence of the plasma fibrinogen concentration is small, and the assay is not affected by exercise‐induced changes in the plasma plasminogen‐activator level. Using this technique the range of HF co‐factor in the plasma of 20 healthy subjects was found to lie between 76 and 150% of pooled normal plasma.