Persistent C‑peptide secretion is associated with favourable CGM metrics in adults with type 1 diabetes – Published online 30/10/2025
Roland H. Stimson, Anna R. Dover, Catriona Clarke, Carina Conceicao, Lindsay McDonald, Lucy Miller, Helen Wise, Shareen Forbes, Rohana J. Wright, Marcus J. Lyall, Mark W. J. Strachan, Fraser W. Gibb
A proportion of individuals with type 1 diabetes retain measurable residual endogenous insulin secretion, reflected by detectable C-peptide levels, and this has been linked to improved glycaemic outcomes and reduced risk of diabetes-related complications. In this issue, Stimson et al (https://doi.org/10.1007/s00125-025-06578-1) present findings from a real-world cohort of 945 adults with type 1 diabetes. In their study, routine random plasma C-peptide testing revealed that preserved beta cell function was strongly associated with favourable continuous glucose monitoring (CGM) metrics. C-peptide persistence was associated with greater time in range, lower time below range, reduced glucose variability, less extreme hyperglycaemia and lower HbA1c. Crucially, the authors found that differences in CGM metrics emerged above a threshold of around 50 pmol/l, suggesting the lower limit at which residual insulin secretion is clinically relevant. Shorter duration of diabetes, older age, male sex and non-smoking status were independently associated with C-peptide persistence. Even 10 to 15 years after diagnosis, almost 40% of participants had persistent C-peptide secretion. The authors conclude that these findings support both the value of C-peptide testing in routine clinical care and the potential impact of treatments that preserve endogenous secretion.
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