A radioimmunoassay method for the measurement of plasma insulin is described relying on activated charcoal for the separation of free and bound fractions. The technique illustrates the application of theoretical precepts designed to maximise assay precision in all radioimmunoassay and other saturation assay techniques.
In addition, because particular emphasis has been placed on ensuring that, as far as is possible, all incubation mixtures are similar as possible other than in hormone concentration, non-specific effects appear to have been essentially eliminated. The technique yields a mean normal fasting value of 5.3μU/ml (range 2–14 μU/ml). Its sensitivity is such that 10 μl samples of serum (or plasma) may be assayed.