Measurement of Peak C-Peptide at Diagnosis Informs Glycemic Control but not Hypoglycemia in Adults With Type 1 Diabetes

Context: High-residual C-peptide in longer-duration type 1 diabetes (T1D) is associated with fewer hypoglycemic events and reduced glycemic variability. Little is known about the impact of C-peptide close to diagnosis. Objective: Using continuous glucose monitoring (CGM) data from a study of newly diagnosed adults with T1D, we aimed to explore if variation in C-peptide close to diagnosis influenced glycemic variability and risk of hypoglycemia. Methods: We studied newly diagnosed adults with T1D who wore a Dexcom G4 CGM for 7 days as part of the Exercise in Type 1 Diabetes (EXTOD) study. We examined the relationship between peak stimulated C-peptide and glycemic metrics of variability and hypoglycemia for 36 CGM traces from 23 participants. Results: For every 100 pmol/L-increase in peak C-peptide, the percentage of time spent in the range 3.9 to 10 mmol/L increased by 2.4% (95% CI, 0.5-4.3), P = .01) with a reduction in time spent at level 1 hyperglycemia (> 10 mmol/L) and level 2 hyperglycemia (> 13.9 mmol/L) by 2.6% (95% CI, -4.9 to -0.4, P = .02) and 1.3% (95% CI, -2.7 to -0.006, P = .04), respectively. Glucose levels were on average lower by 0.19 mmol/L (95% CI, -0.4 to 0.02, P = .06) and SD reduced by 0.14 (95% CI, -0.3 to -0.02, P = .02). Hypoglycemia was not common in this group and no association was observed between time spent in hypoglycemia (P = .97) or hypoglycemic risk (P = .72). There was no association between peak C-peptide and insulin dose-adjusted glycated hemoglobin A1c (P = .45). Conclusion: C-peptide is associated with time spent in the normal glucose range and with less hyperglycemia, but not risk of hypoglycemia in newly diagnosed people with T1D.The article is available via Open Access. Click on the 'Additional link' above to access the full-text.Accepted version, submitted versio