Determination of human plasma kininogen by a single radial immunodiffusion method and the bradykinin equivalent.

An SRI method is presented for the quantitation of native human plasma kininogen using a monospecific high avidity antiserum prepared against the conformational determinants of kininogen heavy chain (HC antigen). The SRI value of total human plasma kininogen averaged 0.260 +/- 0.052 g/l (+/- 2 SD) using a standard curve of normal human plasma in each assay (measuring range 0.016-0.260 g/l). The SRI data, confirmed by RIA, were compared with determination of the bradykinin equivalent by bioassay 4.30 +/- 0.052 mg/l (+/- 2 SD), generally accepted as a measure of total plasma kininogen. The SRI method does not discriminate between LMr and HMr kininogen but detects an increase of total kininogen independently of bradykinin release as a consequence of activated proteolysis. It is suggested that the SRI method can be applied to study levels of kininogen in clinical research.