Preserved C-peptide is common and associated with higher time in range in Chinese type 1 diabetes

Objective The aim of this study is to determine the residual C-peptide level and to explore the clinical significance of preserved C-peptide secretion in glycemic control in Chinese individuals with type 1 diabetes (T1D). Research design and methods A total of 534 participants with T1D were enrolled and divided into two groups, low–C-peptide group (fasting C-peptide ≤10 pmol/L) and preserved–C-peptide group (fasting C-peptide 10 pmol/L), and clinical factors were compared between the two groups. In 174 participants who were followed, factors associated with C-peptide loss were also identified by Cox regression. In addition, glucose metrics derived from intermittently scanned continuous glucose monitoring were compared between individuals with low C-peptide and those with preserved C-peptide in 178 participants. Results The lack of preserved C-peptide was associated with longer diabetes duration, glutamic acid decarboxylase autoantibody, and higher daily insulin doses, after adjustment OR, 1. 10 interquartile range (IQR), 1. 06–1. 14; OR, 0. 46 (IQR, 0. 27–0. 77) ; OR, 1. 04 (IQR, 1. 02–1. 06). In the longitudinal analysis, the percentages of individuals with preserved C-peptide were 71. 4%, 56. 8%, 71. 7%, 62. 5%, and 22. 2% over 5 years of follow-up. Preserved C-peptide was also associated with higher time in range after adjustment of diabetes duration 62. 4 (IQR, 47. 3–76. 6) vs. 50. 3 (IQR, 36. 2–63. 0) %, adjusted P = 0. 003. Conclusions Our results indicate that a high proportion of Chinese patients with T1D had preserved C-peptide secretion. Meanwhile, residual C-peptide was associated with favorable glycemic control, suggesting the importance of research on adjunctive therapy to maintain β-cell function in T1D.