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), = .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, = .02) and 1.3% (95% CI, -2.7 to -0.006, = .04), respectively. Glucose levels were on average lower by 0.19 mmol/L (95% CI, -0.4 to 0.02, = .06) and SD reduced by 0.14 (95% CI, -0.3 to -0.02, = .02). Hypoglycemia was not common in this group and no association was observed between time spent in hypoglycemia ( = .97) or hypoglycemic risk ( = .72). There was no association between peak C-peptide and insulin dose-adjusted glycated hemoglobin A ( = .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