A soluble-phase proinsulin radioimmunoassay and its use in diagnosis of hypoglycaemia.
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.
Naylor
B A
BA
Diabetes Research Laboratories, Radcliffe Infirmary, Oxford, UK.
Matthews
D R
DR
Turner
R C
RC
D000328:Adult; D000918:Antibody Specificity; D002096:C-Peptide / Q000097:blood / Q000276:immunology; D003920:Diabetes Mellitus / Q000097:blood; D005260:Female; D006801:Humans; D007003:Hypoglycemia / Q000097:blood / Q000175:diagnosis*; D007106:Immune Sera / Q000276:immunology; D007328:Insulin / Q000097:blood / Q000276:immunology; D008297:Male; D011384:Proinsulin / Q000097:blood* / Q000276:immunology; D011863:Radioimmunoassay / Q000379:methods; D012015:Reference Standards
D002096:C-Peptide; D007106:Immune Sera; D007328:Insulin; D011384:Proinsulin