Persistent C-peptide secretion is associated with favourable continuous glucose monitoring (CGM) metrics in adults with type 1 diabetes
Authors' conclusion
Random C-peptide measurement in routine care identifies adults with type 1 diabetes who are more likely to achieve CGM and HbA1c targets. Differences in glycaemic metrics are clinically meaningful at thresholds ≥100 pmol/l. These findings support efforts to preserve residual beta cell function and highlight the potential value of C-peptide in individualising therapy.
Study context
- Population
- Adults with T1D at a single UK centre; diabetes duration >1 year, random plasma glucose >4 mmol/l at C-peptide sampling, ≥70% Freestyle Libre 2 CGM data completeness; median age 45 years, 54% male
- Participants
- 945 adults
- Exposure
- C-peptide categories
- Outcome
- Relationship between random plasma C-peptide levels and CGM metrics
Methodological detailssingle-centre, real-world cohort
- Single-centre
- Real-world cohort
Main finding
As reported in the abstract
CGM metrics by C-peptide category
- TBR: C-peptide <50 pmol/l vs 101-200 pmol/l (median [IQR])
- 2% [1-5] vs 1% [0-3]
- Glucose CV: C-peptide <50 pmol/l vs 101-200 pmol/l
- 37.5% [34.2-42.0] vs 32.5% [29.0-36.6]
- TIR: C-peptide <50 pmol/l vs 50-100 pmol/l
- 45.0% [32.0-61.0] vs 55.0% [37.0-66.5]
- Time above 13.9 mmol/l: C-peptide <50 pmol/l vs 50-100 pmol/l
- 20.0% [9.0-36.0] vs 10.0% [5.5-31.5]
- All pairwise comparisons
- p<0.05
- C-peptide ≥100 pmol/l independently associated with TBR <4%
- OR 5.4, p<0.001
Observational data: associations, not effects.
Further findings
HbA1c <53 mmol/mol (7%)
- C-peptide ≥100 pmol/l associated with achieving HbA1c <53 mmol/mol (7%)
- OR 1.8, p=0.043
Factors associated with higher C-peptide
- Shorter diabetes duration
- OR 0.87 per year, p<0.001
- Older age at diagnosis
- OR 1.04 per year, p<0.001
- Male sex
- OR 1.44, p=0.042
C-peptide <10 pmol/l vs 10-49 pmol/l
- No significant glycaemic differences
Original publication
Persistent C-peptide secretion is associated with favourable CGM metrics in adults with type 1 diabetes. Diabetologia. Published 30 October 2025. doi:10.
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