A direct two-site peroxidase-based enzyme-linked immunosorbent assay for proinsulin.

A non-competitive sandwich assay using an anti-C-peptide IgG and an anti-insulin IgG was developed to measure fasting levels of proinsulin in human serum. The former antibody provided the lower layer in a sandwich immunoassay, the upper layer being composed of an anti-insulin IgG-horse radish peroxidase conjugate. The assay showed negligible cross reactivity at supraphysiological levels of insulin and C-peptide. The method enabled the estimation of proinsulin in fasting non-diabetic control subjects [13.7 +/- 1.6(4) pM] and in type 2 non-insulin-dependent diabetic patients [23.2 +/- 1.1(8) pM].