Radioimmunoassay of trypsin-like substance in human serum.

A radioimmunological method for circulating trypsin-like substances was set up, using cathodic trypsin (isolated from human pancreas) as immunogen, reference standard and material to label, and bovine serum to stabilize the system. The assay scheme included a bound-free separation by polyethylene-glycol precipitation after a 1-h incubation at room temperature. Some relevant points emerged from the validation experiments: a) the assay proved simple and reliable, meeting both requirements of a prompt clinical response and of a high sensitivity level (1.5 ng/ml or less); b) evidence was added to the view that cathodic trypsinogen is the immunoassayable species present in the blood stream; c) the parallelism of the radioimmunological responses of cathodic trypsin and trypsinogen demonstrated that a self-consistent analytical information may be derived using either references; d) the absence of detectable amounts of trypsin-like substances in sera from totally-pancreatectomized patients (3 cases) indirectly confirmed the organ-specificity of the measurement; e) a "normal" level of 27 +/- 8 ng trypsin equivalent/ml (X +/- SD, n = 82) resulted: some much higher literature data, all related to a single radioimmunoassay system (RIA-Gnost trypsin kit, Hoechst, FRG), are seemingly explained by the different purity observed for the reference materials.