Postprandial C-Peptide to Glucose Ratio as a Promising Systemic Marker of Diabetic Retinopathy in Type 2 Diabetes.

Purpose: The purpose of this study was to assess the association between C-peptide (CP)-related parameters and diabetic retinopathy (DR) in type 2 diabetes mellitus (T2DM), and find a superior parameter in predicting DR.

Methods: One thousand seventy-eight patients with T2DM were included in this cross-sectional study. Fasting and postprandial CP (FCP and PCP), delta CP, FCP, or PCP to glucose ratio (FCGR and PCGR), homeostasis model assessment of β-cell function (HOMA-B), and insulin resistance (HOMA-IR) were compared among different stages of DR. Odds ratios (ORs) of these indices for the presence and severity of DR were estimated after adjusting for confounding factors. Multivariate logistic analysis was performed to evaluate the association between PCGR and DR according to PCGR quartiles. Receiver operating characteristic (ROC) curves were generated to determine the discriminative power of DR.

Results: Among CP-related indices, PCGR showed the most significant association with mild and moderate nonproliferative DR (NPDR; per SD increase, OR = 0.44, P < 0.001), and vision-threatening DR (VTDR; OR = 0.09, P < 0.001). When grouped by PCGR quartiles, patients in the lower quartile showed a higher risk of developing DR. PCGR was negatively associated with DR and VTDR independent of confounders (Pfor trend < 0.001). PCGR had high predictive abilities of DR and VTDR (area under the curve [AUC] = 0.76 and 0.83), and also increased the AUC values of the standard model.

Conclusions: Compared with insulin resistance (IR), DR was more associated with impaired β-cell function. PCGR could be a promising systemic marker for determining patients with T2DM at high risk of developing DR, especially VTDR.

Translational relevance: PCGR could be a promising marker of DR assisting individualized management of T2DM patients.