Metabolic impact of residual C-peptide secretion in type 1 diabetes mellitus

Objective: This study aimed to evaluate the association of detectable C-peptide levels with various continuous glucose monitoring (CGM) metrics and diabetes complications in patients with type 1 diabetes mellitus (T1DM). Subjects and methods: Retrospective, descriptive study of 112 patients with T1DM undergoing intensive insulin therapy, categorized according to fasting C-peptide level into undetectable (<0.05 ng/mL) and detectable (>= 0.05 ng/mL) groups. Results: The patients' median age at diagnosis was 22 (12-34) years and the median T1DM duration was 18.5 (12-29) years. Patients with detectable versus undetectable C-peptide levels were older (27.5 [16.5-38.5] versus 17.5 [9.8-28.8] years, respectively, p = 0.002) and had shorter disease duration (14 [9-24] versus 20 [14-32] years, respectively, p = 0.004). After adjustment for covariates (sex, disease duration, body mass index, and use of continuous subcutaneous insulin infusion), detectable C-peptide level was associated with lower time above range (TAR; a beta -11.03, p = 0.002), glucose management indicator (GMI, a beta -0.55, p = 0.024), and average glucose (a beta -14.48, p = 0.045) and HbA1c (a beta -0.41, p = 0.035) levels. Patients with detectable versus those with undetectable C-peptide level had significantly higher time in range (TIR) before (beta = 7.13, p = 0.044) and after (a beta = 11.42, p = 0.001) adjustments. Detectable C-peptide level was not associated with lower time below range (TBR), coefficient of variation (CV), or prevalence of chronic microvascular and macrovascular complications. Conclusions: Persistent C-peptide secretion in patients with T1DM was associated with significantly better metabolic control reflected by different glucose metrics, namely, TIR, TAR, GMI, and HbA1c.