Background and Aims: High residual C-peptide in longer duration type 1 diabetes associates with fewer hypoglycemic events and reduced glycemic variability. However, little is known about the impact of C-peptide close to diagnosis. Using continuous glucose monitoring (CGM) data from a study of newly diagnosed adults with type 1 diabetes, we aimed to explore if variation in C-peptide close to diagnosis influenced glycemic variability and risk of hypoglycaemia.

Materials and Methods: We studied newly diagnosed adults with type 1 diabetes who wore a Dexcom G4 CGM as part the EXTOD study. We examined the relationship between peak stimulated C-peptide in a mixed meal tolerance test and glycemic metrics of variability and hypoglycemia for 36 CGM traces from 23 participants.

Results: Higher levels of C-peptide associated with lower glycemic variability, more time in range and less hyperglycemia. For every 100 pmol/L increase in peak C-peptide, percentage time spent in the range 3.9-10 mmol/L was increased by 2.39% [95% CI: 0.51,4.26], p=0.012) with a reduction in time spent in level 1 hyperglycaemia (> 10 mmol/L) and level 2 hyperglycemia (> 13.9 mmol/L) glucose levels by 2.64% [95% CI: -4.87, -0.41, p=0.018) and 1.33% [95% CI: -2.66, -0.0057], p= 0.041) respectively. Glucose levels were on average lower by 0.19 mmol/L ([95 % CI: -0.39,0.015], p=0.06) and standard deviation reduced by 0.14 [95% CI: -0.25, -0.023], p=0.017) for every 100 pmol/L increase in peak C-peptide. Hypoglycemia was not common in this group and no association was observed between time spent in hypoglycemia (p=0.967) or hypoglycemic risk (p=0.721). There was no association between peak C-peptide and insulin dose (p=0.707), HbA1C (p=0.364) or insulin dose adjusted HbA1c (IDAA1c, p=0.452).

Conclusion: C-peptide associates with time spent in normal glucose range and with less hyperglycemia, but not risk of hypoglycemia in newly diagnosed people with type 1 diabetes.


A. Carr: None. R. A. Oram: Consultant; Self; Janssen Research & Development, LLC. P. Narendran: Speaker’s Bureau; Self; Novo Nordisk Inc., Sanofi. R. C. Andrews: None.

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