We performed this study to identify factors related to intact incretin levels in patients with type 2 diabetes mellitus (T2DM).

We cross-sectionally analyzed 336 patients with T2DM. Intact glucagon-like peptide 1 (iGLP-1) and intact glucose-dependent insulinotropic polypeptide (iGIP) levels were measured in a fasted state and 30 minutes after ingestion of a standard mixed meal. The differences between 30 and 0 minute iGLP-1 and iGIP levels were indicated as ΔiGLP-1 and ΔiGIP.

In simple correlation analyses, fasting iGLP-1 was positively correlated with glucose, C-peptide, creatinine, and triglyceride levels, and negatively correlated with estimated glomerular filtration rate. ΔiGLP-1 was positively correlated only with ΔC-peptide levels. Fasting iGIP showed positive correlations with glycosylated hemoglobin (HbA1c) and fasting glucose levels, and negative correlations with ΔC-peptide levels. ΔiGIP was negatively correlated with diabetes duration and HbA1c levels, and positively correlated with Δglucose and ΔC-peptide levels. In multivariate analyses adjusting for age, sex, and covariates, fasting iGLP-1 levels were significantly related to fasting glucose levels, ΔiGLP-1 levels were positively related to ΔC-peptide levels, fasting iGIP levels were related to fasting C-peptide levels, and ΔiGIP levels were positively related to ΔC-peptide and Δglucose levels.

Taken together, intact incretin levels are primarily related to C-peptide and glucose levels. This result suggests that glycemia and insulin secretion are the main factors associated with intact incretin levels in T2DM patients.