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A soluble-phase proinsulin assay has been developed which does not require solid-phase antibody-binding. A human proinsulin standard curve is prepared in insulin-free and proinsulin-free plasma for comparison with unknown plasma samples. Proinsulin and insulin are bound with excess anti-insulin antiserum, and free C-peptide is removed by charcoal adsorption. The supernatant is then assayed using a routine C-peptide radioimmunoassay which utilises anti-C-peptide antiserum. The sensitivity of the assay (2 standard deviations above zero) is 9 pmol/L using 200 microL plasma sample. The assay is free from insulin cross-reactivity up to 100 mU/L and C-peptide up to 2000 pmol/L. Between-assay CV is 13% at 100 pmol/L. The assay has been used in subjects with hypoglycaemia of various aetiologies and has shown that a raised plasma proinsulin in the presence of hypoglycaemia can occur in sulphonylurea-induced and reactive hypoglycaemia as well as in insulinomas. After hyperglycaemic clamps at 7.5, 10 and 15 mmol/L glucose, type II diabetics both on and off sulphonylurea, were found to have lower proinsulin concentrations compared with normal subjects, commensurate with the diabetics' lower insulin responses.

Original publication

DOI

10.1177/000456328702400404

Type

Journal article

Journal

Ann Clin Biochem

Publication Date

07/1987

Volume

24 ( Pt 4)

Pages

352 - 363

Keywords

Adult, Antibody Specificity, C-Peptide, Diabetes Mellitus, Female, Humans, Hypoglycemia, Immune Sera, Insulin, Male, Proinsulin, Radioimmunoassay, Reference Standards