SOME FACTORS OF SIGNIFICANCE IN THE DOUBLE ANTIBODY IMMUNOASSAY OF INSULIN

Abstract

ABSTRACT Differences were demonstrated between 4 insulin antibody (guinea pig) precipitating antisera (rabbit), int. al. in their ability to cross react with human γ-globulin components. This cross reaction is presumably the reason why »negative« insulin values can be found at higher concentrations of certain precipitating antisera. Independently of the precipitating antiserum it was possible, in some cases, to demonstrate a difference between the insulin concentration in serum and in heparinized plasma. This difference could be eliminated by the addition of heparin, by long-lasting freezing, and by dilution of the serum. Hence, the higher values found in certain cases in serum, as compared with plasma are presumably due to the presence of complement. It is essential in the use of the double antibody technique for the determination of insulin in plasma and serum that a heparin preparation with anti-complement activity should be used and that the concentration range of the precipitating antiserum should be fixed. The double antibody method can be used with or without pre-precipitation if the above mentioned criteria are fulfilled. Pre-precipitation, however, is to be preferred, as the precipitation reaction here occurs under constant conditions.