Determination of Hageman Factor (HG, Factor XII) and Plasma Prekallikrein (Fletcher Factor) by Radioimmunoassays

Abstract

The titers of components of the plasma kallikrein-kinin system have been measured conventionally by their biological functions. The functional assays are, however, antagonized by the presence of inhibitors and/or the absence of potentiators in test samples. Immunologic assays obviate these difficulties. We have developed specific, sensitive and reproducible radioimmunoassays (RIA) for HF and prekallikrein, and have applied these assays to some clinical conditions. Normal pooled human plasma contained approximately 40 μg of HF and 50 μg of prekallikrein per ml. RIA were able to measure concentrations of HF and prekallikrein as low as 0.1% and 0.3% that of normal pooled plasma respectively. A good correlation existed between titers measured by clotting and radioimmunoassays among 40 normal subjects (correlation co-efficient = 0.82 for HF and 0.71 for prekallikrein). There was no significant difference between the levels of HF and prekallikrein in plasma and those in serum. Both HF and prekallikrein were significantly reduced in plasmas of patients with advanced liver cirrhosis or disseminated intravascular coagulation (DIC) and in cord serums, but they were normal in plasmas obtained after strenuous physical exercise and in plasmas of patients under treatment with warfarin.