Background for development of improved and new RIAs for insulin, C-peptide and proinsulin

Abstract

In the mid-sixties when it was gradually accepted that insulin could be measured fairly accurately in serum many laboratories established RIAs based on the principles of the pioneers. It became mandatory to improve several of the steps in order to obtain routine methods — especially the separation of free and antibody-bound insulin — to replace Berson and Yalow’s chromato-electrophoresis. Secondly, there was a need for a routine method to extract and isolate insulin from serum of insulin treated diabetics having insulin antibodies (Ab₁). Most of the IRI in serum from such patients is bound to Ab₁ while a minor part is free IRI. The extraction procedure should lead to isolation of the free and bound IRI clearly separated from the Ab₁. The bound insulin is closely related to the antibody level^61,121 and gives more exact information about the immunogenicity of the insulin preparations than the mere percentage of bound ¹²⁵I-insulin obtained after addition of a randomly selected amount of tracer^19,125. In addition, it became of interest to characterize the total IRI circulating which could, in theory, consist of a mixture of insulins and proinsulins⁵⁶.