The average 30-minute post-prandial C-peptide predicted diabetic retinopathy progress: a retro-prospective study

Background The conclusion between Connecting peptide (C-peptide) and diabetic chronic complication was controversial. The purpose of this study is to explore the possible association between average C-peptide with diabetic retinopathy (DR) progression in Chinese patients with type 2 diabetes. Methods This is a retro-prospective study. 622 patients with type 2 diabetes were included. DR was evaluated using non-mydriatic fundus photography and DR progression was defined as any deterioration of either eye. Fasting and postprandial c-peptide levels were assayed at baseline and follow-up period. Differences between continuous variables were compared using the Mann–Whitney U test; and categorical variables were analyzed by the chi-square test. Correlation between parameters and 30-minute postprandial C-peptide were determined by Spearman correlation test. The relationship between C-peptide and DR progression was evaluated by multivariable binary logistic regression. Two-tailed P-values < 0.05 were regarded as statistically significant. Results DR was present in 162 (26.0%) patients at baseline, and 26.4% of patients were found progression of DR at follow-up. Patients with progression of DR had lower average levels of 30-minute postprandial C-peptide (2.01 ng/ml vs. 2.6 ng/ml, p = 0.015) and 120-minute postprandial C-peptide (3.17 ng/ml vs. 3.92 ng/ml, p < 0.029), as well as average increment of 30-minute (0.41 ng/ml vs. 0.64 ng/ml, p = 0.015) and 120-minute postprandial C-peptide (1.48 ng/ml vs. 1.93 ng/ml, p < 0.017), than those without DR aggravation. Multivariate logistic regression analysis determined that 30-minute postprandial C-peptide and its increment were related to reduced odds ratios for DR progression (odds ratios [OR] = 0.83 and 0.74, respectively). Conclusion Our results suggest that the Average 30-minute post-prandial C-peptide and increment were negatively correlated with DR progression, which further demonstrates the importance to preserve β-cell residual function in the prevention for DR progression. Trial registration Not applicable.