C-peptide and insulin secretion in diabetes mellitus treated with oral hypoglycaemic agents or diet alone. A 3 years epidemiological cohort study on the Island of Falster, Denmark.

In a 3 yr epidemiological cohort study of 273 diabetics treated with oral hypoglycaemic agents (OHA) and 60 diet-treated diabetics the predictive value of fasting plasma C-peptide levels was assessed with the attempt to discriminate between insulin dependence and non-insulin dependence. Serum insulin, blood glucose, haemoglobin AI, bicarbonate, urine for ketone bodies, height and weight were measured too. All but 8 OHA-treated patients (97%) had fasting C-peptide greater than 0.40 pmol/ml at both investigations. Six had C-peptide in the interval 0.21-0.40 pmol/ml at both investigations and 2 a C-peptide less than or equal to 0.20 pmol/ml all of which became insulin dependent during the 3 yr period. The highest fasting C-peptide concentrations were found in overweight diabetics with a blood glucose level greater than 8.5 mmol/l. Overweight diabetics had significantly elevated fasting insulin compared to the normal weights but when the IRI concentrations were corrected by the body mass index hyperinsulinaemia was positively correlated with high levels of blood glucose and haemoglobin AI, i.e. poor glycaemic control and not with overweight. The results suggest that determination of fasting plasma C-peptide can be an additional clinical help in discriminating between insulin dependence and non-dependence.