Factors affecting and patterns of residual insulin secretion during the first year of Type 1 (insulin-dependent) diabetes mellitus in children

Summary We measured serum C-peptide, glucose, pH, islet antibodies and insulin antibody binding at diagnosis in 84 children with Type 1 (insulin-dependent) diabetes. In a subgroup of 33 children, residual insulin secretion (basal and peak C-peptide response to Sustacal), insulin antibody binding and HbA_1c were measured at 10 days, 1, 3, 6 and 12 months. At presentation C-peptide correlated positively with age at onset and negatively with the blood glucose concentration. Median C-peptide concentration at diagnosis was low, rose significantly (p<0.05) at 10 days, reached a maximum at 1–3 months and declined gradually to 1 year. C-peptide concentration both at diagnosis and at 10 days correlated with that at 3 and 6 months. Of the factors investigated, only age (p<0.005) and sex (higher in females, p<0.01) were found to have a significant influence on basal/peak C-peptide levels throughout the first year. In particular there was no relationship between C-peptide, HbA_1c and insulin dose during this period. A peak C-peptide response at 3–6 months>/<0.32 nmol/l was used to divide the group into two: 16 had a peak response <0.32 nmol/l (low secretors) while in 17, the peak C-peptide was >0.32 nmol/l (high secretors). While the low secretors had significantly (p<0.05) lower C-peptide levels during the first year, there were no differences between low and high secretors in HbA_1c or insulin dose. These data suggest that there are two patterns of residual insulin secretion during the first 12 months after diagnosis of Type 1 diabetes. One pattern shows good amplitude and duration of residual insulin secretion, while both these features are significantly (p<0.05) reduced in the other. The C-peptide concentration both at diagnosis and at 10 days, as well as age at onset and sex are important predictors of the pattern to be followed. Our data suggest further that the magnitude of residual insulin secretion does not play a decisive role in metabolic control during this period.