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

Aims: 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. Methods: 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. Results: 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%). Conclusions: 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.