Diabetes mellitus in cats is generally treated using insulin therapy. The licensed insulin preparations in the UK are either of porcine (Caninsulin®, Intervet UK Ltd, Milton Keynes, UK) or bovine (Insuvet®, Schering Plough Animal Health, Uxbridge, UK) origin. Since both of these differ from feline insulin, treatment using either preparation is likely to stimulate an immune response. It has been suggested that the presence of anti-insulin antibodies might interfere with diabetic stabilisation and management. The aim of the current study was to investigate and compare the prevalence of anti-insulin antibodies in diabetic cats treated with different insulin preparations.

Serum was collected from 60 insulin-treated diabetic cats. This diabetic group comprised 23 cats treated with Caninsulin, 13 cats treated with Insuvet Lente and 24 cats treated with Insuvet PZI (protamine zinc bovine insulin). Serum samples from 50 non-diabetic cats were used as controls. Antibody levels against porcine insulin, bovine insulin and protamine were determined by enzyme-linked immunosorbent assay (ELISA).

Serological reactivity was similar regardless of whether porcine or bovine insulin was used as the antigen in the ELISA. There was a significant difference in anti-insulin antibodies between the control and insulin-treated diabetic group (P<0.001), with 12 of 60 diabetic cats (i.e., 20%) positive for anti-insulin antibodies. There was no significant difference between the different insulin-treated groups. Five of 23 cats receiving Caninsulin, 3 of 13 cats receiving Insuvet Lente and 4 of 24 cats receiving Insuvet PZI showed insulin antibody reactivity. There was no significant difference in antibody reactivity to protamine, comparing non-diabetic and diabetic cats and comparing different insulin-treated groups.

In contrast to the situation in dogs, these results demonstrate a low prevalence of anti-insulin antibodies in insulin-treated diabetic cats with no difference seen between Insuvet and Caninsulin therapy. Surprisingly, administration of protamine zinc insulin did not seem to stimulate anti-protamine antibodies and in fact some control cats demonstrated antibodies against this protein, possibly as the result of exposure in the diet. Further work is needed to investigate the clinical significance of anti-insulin antibodies in treated diabetic cats.