Measurement of Insulin in Human Sera Using a New RIA Kit. 1. Insulin Determination in the Absence of Insulin Antibodies — Conventional Assay and Micro Modification²)

Summary

A sensitive and versatile radioimmunoassay (RIA) for insulin was established using human insulin standard, a specific guinea pig anti-insulin antiserum and rabbit anti-guinea pig serum. Radioiodination was performed according to a modified chloraimine T method. Tracer preparations were used for as long as 6 weeks after iodination. The standard curve ranges from 0.044 to 1.2 nmol/l. The intra-assay coefficient of variation (CV) was 3— 5% and the inter-assay CV was 6—9% in the optimal range between 0.4 and 0.9 nmol/l. The average recovery of human insulin added to plasma or serum samples was 100.2 ± 2.0% (n = 38) and 100.1 ± 1.9 % (n = 42), respectively.

In addition to human insulin, porcine, canine, rabbit and bovine insulin can also be determined but not rat or mouse insulin. The cross-reactivity of the antiserum with porcine proinsulin was found to be 40% on the molar basis. The range of mean fasting plasma insulin concentrations in healthy subjects and under various pathological conditions were estimated.

Key words

Insulin - Radioimmunoassay - Kit - Diabetes mellitus - Plasma insulin concentrations