The utility of assessing C-peptide in patients with insulin-treated type 2 diabetes: a cross-sectional study

We aimed at evaluating residual β-cell function in insulin-treated patients with type 2 diabetes (T2D) while determining for the first time the difference in C-peptide level between patients on basal-bolus compared to those on the basal insulin scheme, considered as an early stage of insulin treatment, together with assessing its correlation with the presence of complications.

A total of 93 candidates with T2D were enrolled in this cross-sectional study and were categorized into two groups based on the insulin regimen: Basal-Bolus (BB) if on both basal and rapid acting insulin, and Basal (B) if on basal insulin only, without rapid acting injections. HbA1c, fasting C-peptide concentration and other metabolic parameters were recorded, as well as the patient medical history.

The average fasting C-peptide was 1.81 ± 0.15 ng/mL, and its levels showed a significant inverse correlation with the duration of diabetes (r = -0.24, p = 0.03). Despite similar disease duration and metabolic control, BB participants displayed lower fasting C-peptide (p < 0.005) and higher fasting glucose (P = 0.01) compared with B patients. Concentrations below 1.09 ng/mL could predict the adoption of a basal-bolus treatment (Area 0.64, 95%CI:0.521-0.759, p = 0.038, sensitivity 45% and specificity 81%).

Insulin-treated patients with long-standing T2D showed detectable level of fasting C-peptide. Measuring the β-cell function may therefore guide toward effective therapeutic options when oral hypoglycemic agents prove unsuccessful.