Quantitation of Free, Total, and Antibody-bound Insulin in Insulin-Treated Diabetics

Abstract

We describe a simplified method for measuring free, total, and antibody-bound insulin in insulin-treated patients in whom antibodies to insulin are present. The free, active insulin is extracted from the serum with a polyethylene glycol solution. Total insulin is extracted from the serum with a polyethylene glycol solution after dissociation of the antibody—antigen complex with dilute HCl. Aliquots of the extracts are used in the radioimmunoassay system. The figure for antibody-bound insulin is the difference between the total and free insulin values and reflects the concentration of insulin antibodies present. A commercially available ("Phadebas") radioimmunoassay for immunoreactive insulin was used to quantitate the insulin present in the two extracts. Recovery of added insulin averaged 85% for the free insulin and 87% for the total insulin.