Serum
C-peptide concentrations were determined in 121 elderly subjects: 25 nondiabetic controls aged 69-86 years, and 96 type
2 (noninsulin-dependent diabetes mellitus) diabetics aged 64-96 years. Forty-seven of the diabetics were treated with
tablets, 35 with
insulin, and 14 with diet alone. Fasting serum
C-peptide concentrations (nmol/l; mean +/- SD) were 0.51 +/- 0.20 for controls; 0.60 +/- 0.16 for diabetics on diet alone; 0.72 +/- 0.33 for diabetics on
tablets and 0.46 +/- 0.23 for diabetics on
insulin (p less than 0.001 for diabetics on
tablets vs. controls and diabetics on
tablets vs. diabetics on
insulin). The
glucagon-stimulated
C-peptide concentrations were similar in all groups; the increment after
glucagon was less in the diabetic patients on
tablets or on
insulin than in the nondiabetics. In 10 patients on
insulin treatment and with fasting
C-peptide of 0.24-1.46 nmol/l an attempt was made to withdraw
insulin. In 4 subjects the transfer to
tablets was possible. Serum
C-peptide level did not predict the outcome of the attempt to change the
therapy, but the possibility of an adequate dietary regimen seemed to be important. The results demonstrate a wide range of basal
C-peptide concentrations in elderly diabetics on different treatments, which may indicate varying pathogenetic contributions of
insulin deficiency and resistance in these patients. Our observations emphasize the necessity for regular re-evaluation of the therapeutic management of elderly diabetic patients.