High molecular weight kininogen assay

A chromogenic assay for functional high molecular weight kininogen (HMWK) in a plasma specimen comprising:

• (a) substantially completely inactivating plasma protease inhibitors in a plasma specimen;
• (b) adding soybean trypsin inhibitor, factor XIIa, factor XI and a contact-activating surface to the specimen to form a reaction mixture for the HMWK-dependent activation of factor XI, the amount of soybean trypsin inhibitor added to the specimen being sufficient to establish a molar excess of soybean trypsin inhibitor to prekallikrein in the reaction mixture, the amount of factor XIIa added to the specimen being sufficient to establish a molar excess of factor XIIa to HMWK in the reaction mixture;
• (c) incubating said reaction mixture for a time sufficient to activate not more than about 10% of the factor XI in the reaction mixture to factor XIa;
• (d) preventing further activation of factor XI by adding sufficient corn trypsin inhibitor to the reaction mixture to establish a molar excess of corn trypsin inhibitor to factor XIIa in the reaction mixture;
• and
• (e) assaying the amount of factor XIa formed in the reaction mixture by measuring the hydrolysis of a chromogenic substrate for factor XIa, said amount of factor XIa being directly proportional to the amount of functional HMWK in the plasma specimen.