Relationship between insulin antibodies and metabolic control in type I diabetes mellitus.

1. The objective of the present study was to investigate whether a change in insulin therapy from bovine to purified porcine insulin would result in a decreased level of insulin antibodies (IA) in type I diabetic patients and whether there would be better metabolic control. 2. Insulin antibodies were measured by ELISA. Fifteen type I diabetic patients were prospectively followed for 8 months with monthly evaluations after changing insulin therapy from bovine to purified porcine insulin. 3. Group I patients (N = 4) had IA greater than or equal to 1.5 (value obtained by dividing the ELISA absorbance of the tested serum by the absorbance of a standard serum) at the beginning of the study. For group I patients, the modification of insulin therapy caused a 57% reduction in insulin antibody levels, and this reduction was correlated with a decrease in 24-hour glycosuria (rs = 0.66, P less than 0.001) and glycated protein (rs = 0.65, P less than 0.01). Group II patients (N = 8) had IA less than 1.5 and greater than or equal to 0.3 and group III (N = 3) had IA less than 0.3. Insulin antibody levels were unchanged during the follow-up period in both group II and group III. 4. We also studied endogenous insulin secretion, measured as fasting C-peptide, and its relationships with metabolic control and insulin antibody levels. Patients with residual insulin secretion (C-peptide greater than 60 pmol/l) showed lower levels of 24-h glycosuria, glycated protein and glycated hemoglobin. Furthermore, in this group of patients a negative correlation was found between C-peptide and insulin antibody levels (rs = -0.36, P less than 0.01). 5. We conclude that insulin antibodies could be one of the factors having a detrimental effect on metabolic control.