C-peptide response to oral glucose and its clinical role in elderly people

C-Peptide response to oral glucose was measured in 45 elderly diabetics, in whom final treatment was established on clinical grounds during a 16-18 months follow-up. The diabetic patients comprised 19 ultimately classified as insulin-dependent (IDD) (group 1) and 26 regarded as non-insulin-dependent (NIDD) (group 2). Fifteen matched controls (group 3) and 15 young controls (group 4) were similarly studied. Fasting C-peptide values were lower in groups 1 and 2 (1.48 +/- 0.39 and 2.14 +/- 0.22 ng/ml; mean +/- SEM, respectively) compared with groups 3 and 4 (2.51 +/- 0.16 and 2.71 +/- 0.20 ng/ml, respectively) (p less than 0.001). Peak C-peptide levels were reached at 30 min in healthy young and at 60 min in healthy elderly. All non-diabetic control subjects showed a peak of at least 6.5 ng/ml and an increment of at least 4 ng/ml. The ratio of C-peptide increment/blood glucose increment (100 delta CP/delta BG) at 60 min derived to assess beta-cell function was at least 90 in all healthy subjects. The ratio was less than 10 in 68% of IDD but in only 27% of NIDD patients (p less than 0.01). The 100 delta CP/delta BG was inversely related to the prevailing fasting blood glucose (FBG) (p less than 0.001). These findings suggest that C-peptide response to oral glucose may be a useful test in certain elderly diabetic patients whose insulin dependence is in question.