Factitious diabetes and antibody mediated resistance to beef insulin

A case of factitious diabetes is reported. The patient gave herself insulin intermittently over a four year period. A high concentration of insulin binding antibody was found with the antibody showing much greater avidity towards beef than human insulin. There was resistance to intravenously administered beef insulin with low concentrations of free insulin and high concentrations of bound insulin. In contrast, in response to a glucose tolerance test, both the free insulin and C-peptide responses were normal as was glucose tolerance. The clinical difference in responsiveness to the human and beef insulins is well illustrated in vitro by insulin binding differences and is probably a function not only of different equilibrium constants of the antibody for human and beef insulins but also of different high affinity binding site concentrations.