Analysis of factors influencing postprandial C‐peptide levels in Japanese patients with type 2 diabetes: Comparison with C‐peptide levels after glucagon load

Aims/Introduction: Postprandial serum C‐peptide levels are readily determined in clinical practice and have a good correlation with serum C‐peptide levels after glucagon load; the measurement is often used as an index of endogenous insulin secretion. However, the factors affecting postprandial serum C‐peptide levels remain to be evaluated. Materials and Methods: To investigate the clinical factors affecting postprandial serum C‐peptide, 2‐h postprandial C‐peptide levels after breakfast (PPCPR) were analyzed retrospectively for comparison with glucagon‐stimulated C‐peptide (CPR‐6min) levels measured during hospital admission in 273 Japanese patients with type 2 diabetes. Results: Multiple regression analysis showed that years from diagnosis, body mass index (BMI) and HbA(1c) were the major independent variables predicting PPCPR (R(2) = 0.315). HbA(1c) was a major factor predicting PPCPR, but did not predict CPR‐6min. In addition, HbA(1c) was negatively correlated with PPCPR (r = −0.410, P < 0.0001) and PPCPR/CPR‐6min (r = −0.313, P < 0.0001). Conclusions: PPCPR was correlated with common factors predicting CPR, including years from diagnosis and BMI, but also was negatively correlated with HbA(1c), a unique factor. These results show that chronic elevation of the glucose level might impair endogenous insulin secretion after meal load, but might have little effect on endogenous insulin secretion after glucagon load. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00126.x, 2011)