Plasma C-peptide levels identify insulin-treated diabetic patients suitable for oral hypoglycaemic therapy

Plasma C-peptide levels were measured fasting and 2 h after an oral glucose load in 37 insulin-treated diabetic patients to assess their clinical value in identifying any noninsulin-dependent diabetic patients. All subjects were changed from insulin to oral hypoglycaemic therapy and followed for 3 months. Twenty patients (group A) completed the trial without requiring insulin and 17 (group B) required restabilization on insulin due to deteriorating metabolic control. Fasting and 2 h C-peptide levels were significantly higher in group A (0.11 +/- 0.09 and 0.17 +/- 0.12 nmol/l; mean +/- S.D.) compared with group B (0.02 +/- 0.03 and 0.02 +/- 0.03 nmol/l) (p less than 0.002 and p less than 0.002). The fasting C-peptide levels at 3 months (0.28 +/- 0.14 nmol/l) were also significantly higher than the fasting levels at the beginning of the study (p less than 0.002). Fasting and 2-h glucose levels were lower in group A (11.0 +/- 3.7 and 17.6 +/- 5.2 mmol/l) than in group B (14.4 +/- 6.2 and 23.1 +/- 5.9 mmol/l; p less than 0.05 and 0.02, respectively). The differences in glycosylated haemoglobin and fasting glucose levels at the start of the study and after 3 months of oral therapy were not statistically significant. Although C-peptide values overlapped in groups A and B, they were of greater value in identifying patients suitable for oral therapy than any single clinical criterion, and thus may help in identifying insulin-treated diabetic patients who may be treated with oral therapy without deterioration in metabolic control.