Human
proinsulin and
32-33 split proinsulin have been measured in the peripheral circulation by immunoradiometric assays (IRMAs) and have been shown to be elevated in
impaired glucose tolerance and
non-insulin-dependent diabetes mellitus (
NIDDM). The IRMA for
32-33 split proinsulin did not discriminate between this molecule and des-32 or des-31,32 split
proinsulin. We describe the comparison of IRMA for human plasma
proinsulin and 32-33 split proinsulins with assays combined with high-performance liquid chromatography (HPLC), which can discriminate between 32-33 split, des-32 split, and des-31,32 split
proinsulin. Subjects were those with normal
glucose tolerance (n = 8) and those with
NIDDM (n = 17), who were studied while fasting and 30 min after a
glucose load. After collection, blood was centrifuged promptly, and the serum/plasma was stored frozen until assay. Both IRMA and HPLC methods were calibrated against synthetic
peptides. Interassay coefficients of variation for the IRMA for
proinsulin and
32-33 split proinsulin were < 13% over the ranges 3.8-65 pmol/l and 6.4-65 pmol/l, respectively. The following regression lines were obtained:
proinsulin IRMA = -0.143 + 1.066 HPLC, r = 0.860;
32-33 split proinsulin IRMA = 0.048 + 1.051 HPLC; and des-31,32 split
proinsulin, r = 0.814. For both analytes, there was no significant difference in the relationship of IRMA to HPLC results between the various subject groups and various time points. Thus, the IRMA for
proinsulin has been validated by an independent method.(ABSTRACT TRUNCATED AT 250 WORDS)