title: Immunoluminometric assay (ILMA) for intact human proinsulin and its conversion intermediates.
abstract: We describe an immunoluminometric assay (ILMA) for determination of intact proinsulin and its conversion intermediates. 32,33-split and 65,66-split proinsulin, in human serum. After incubation of the serum samples with the IgG fraction of a guinea pig antiserum against human insulin coated to the surface of polystyrene beads, a sandwich complex was formed using a monoclonal antibody against human C-peptide labelled with acridinium ester as second antibody, yielding a detection limit of 0.11 pmol/l. Mean proinsulin concentration in the serum of 38 healthy fasting subjects was 7.3 pmol/l (S.D. +/- 5 pmol/l, median 5 pmol/l, 95th percentile 15 pmol/l); maximum serum proinsulin after oral glucose stimulation never exceeded 40 pmol/l. Eighteen of 20 patients with confirmed insulinoma had proinsulin concentrations over 50 pmol/l (mean 261 pmol/l, S.D. +/- 248 pmol/l, median 170 pmol/l, 95th percentile 663 pmol/l); serum proinsulin in two patients with completely enucleated B-cell adenoma declined to normal values after surgery.
authors.affiliation: Endocrine Laboratory, Im Breitspiel 15, Heidelberg, Germany.
authors.forename: T M
authors.initials: TM
authors.lastname: Zilkens
authors.forename: A M
authors.initials: AM
authors.lastname: Eberle
authors.forename: H
authors.initials: H
authors.lastname: Schmidt-Gayk
mesh_terms: D006801:Humans; D007118:Immunoassay / Q000379:methods* / Q000592:standards; D008163:Luminescent Measurements; D011384:Proinsulin / Q000097:blood* / Q000592:standards
chemical_list: D011384:Proinsulin