C‐peptide, glycaemic control, and diabetic complications in type 2 diabetes mellitus: A real‐world study

Abstract Objective To explore the relationship between C‐peptide and glycaemic control rate and diabetic complications (microvascular complication and cerebral infarction) and provide evidence for stratified treatment of type 2 diabetes mellitus (T2DM)‐based C‐peptide. Method This is a cross‐sectional real‐world observational study. According to the inclusion and exclusion criteria, we studied 1377 patients with T2DM, grouped by fasting C‐peptide and HOMA‐IR. Blood samples were collected after fasting overnight. Logistic regression was used to analyse the relationship among fasting C‐peptide, HOMA‐IR, C2/C0 ratio (the ratio of 2 h postprandial C‐peptide to fasting C‐peptide), glycaemic control rate, and occurrence of diabetic complications. Restricted cubic spline (RCS) curves based on logistic regression were used to evaluate the relationship between C‐peptide, glycaemic control rate, and diabetic kidney disease (DKD). Results Patients were subdivided according to their fasting C‐peptide in 4 groups (Q1,Q2,Q3,Q4). Patients of group Q3 (1.71 ≤ C‐peptide < 2.51 ng/ml) showed the lowest incidence of DKD, diabetic retinopathy (DR), and rate of insulin absorption as welll as higher glycaemic control rate. Logistic regression shows that the probability of reaching glycemic control increased with higher levels of C‐peptide, compared with group Q1, after adjusting for age, gender, duration of diabetes, body mass index, systolic blood pressure, diastolic blood pressure, creatinine, low‐density lipoprotein, triglyceride, total cholesterol, and high‐density lipoprotein. RCS curve shows that, when C‐peptide is ≤2.68 ng/ml, the incidence of not reaching glycaemic control decreases with increasing C‐peptide. The possibility of not reaching glycaemic control decreased with increasing C2/C0, when C‐peptide is ≥1.71 ng/ml. RCS curve shows that the relationship between C‐peptide and DKD follows a U‐style curve. When C‐peptide is <2.84 ng/ml, the incidence of DKD decreased with increasing C‐peptide. With the increase in the C2/C0 ratio, the incidence of DKD, DR, and fatty liver did not decrease. Conclusion When C‐peptide is ≥ 1.71 and < 2.51 ng/ml, patients with T2DM had a higher glycemic control rate. Excessive C‐peptide plays different roles in DKD and DR; C‐peptide may promote the incidence of DKD but protects patients from DR. Higher C2/C0 ratio is important for reaching glycaemic control but cannot reduce the risk of DKD, DR, and fatty liver.