Analyze of the correlation and corresponding value of serum C-peptide and insulin in adult population

Abstract

Objective: To investigate the correlation between serum C-peptide and in adult population, and establish the corresponding insulin values of serum C-peptide levels. Methods: Cross-sectional study. The clinical data of the adults who underwent physical examination in the Second Medical Center of PLA General Hospital from January 2017 to December 2021 were retrospectively included. The participants were divided into type 2 diabetes group, prediabetes group and normal plasma glucose group according to the diagnostic criteria for diabetes. The correlation between serum C-peptide and insulin was explored by Pearson correlation analysis, linear regression analysis, and nonlinear regression analysis, and the corresponding insulin values of serum C-peptide were established. Results: A total of 48 008 adults were enrolled, including 31 633 males (65.9%) and 16 375 females (34.1%), aged (50.1±9.9) years (18-89 years). There were 8 160 subjects (17.0%) with type 2 diabetes, 13 263 subjects (27.6%) with prediabetes, and 26 585 subjects (55.4%) with normal plasma glucose. The serum fasting C-peptide (FCP, M(Q1, Q3)] of the three groups were 2.76(2.18, 3.47), 2.54(1.99, 3.21) and 2.18(1.71, 2.79)μg/L, respectively. The fasting insulin [FINS, M(Q1,Q3)] of the three groups were 10.98(7.57, 16.09), 10.06(6.95, 14.47) and 8.43(5.86,12.12)mU/L, respectively. FCP was positively correlated with FINS (r=0.82), and 2 h postprandial C-peptide (2 h CP) was positively correlated with 2 h postprandial insulin (2 h INS) (r=0.84) (both P<0.001). FCP was linearly associated with FINS (R2=0.68), and 2 h CP was linearly associated with 2 h INS (R2=0.71) (both P<0.001). There was a power function correlation between FCP and FINS (R2=0.74), and 2 h CP and 2 h INS (R2=0.78) (both P<0.001). The results of the statistical analysis were similar in various glucose metabolism subgroups. Since the fitting degree of the power function model was higher than that of the linear model, the power function model was the best model. The power function equation was FINS=2.96×FCP1.32, and 2 h INS=1.64×(2 h CP)1.60, respectively. Multivariate linear regression analysis demonstrated that FCP was a related factor of FINS (R2=0.70, P<0.001) and 2 h CP was a related factor of 2 h INS (R2=0.73, P<0.001), after adjusting for related confounders. Conclusions: There was a power function correlation between FCP and FINS, 2 h CP and 2 h INS in adult population. The insulin values corresponding to C-peptide levels were established in the study.