Physicians managing type 1 diabetes patients, picture this: a simple random C-peptide blood test revealing who achieves superior glucose control—without insulin. A large real-world UK study uncovers how residual endogenous insulin, measured by C-peptide, dramatically improves CGM metrics and HbA1c targets.
945 Type 1 Adults Reveal C-Peptide's Real Impact
In a study published in the Diabetologia, the researchers analyzed 945 adults with type 1 diabetes (median age 45, diabetes duration 18 years, 54% male, median HbA1c 63 mmol/mol or 7.9%) using Freestyle Libre 2 CGM data. Inclusion required >1 year diabetes duration, random glucose >4 mmol/L at sampling, and ≥70% CGM completeness. C-peptide categories from <50 pmol/L to >400 pmol/L correlated with shorter duration, older diagnosis age, and male sex.
Higher C-Peptide Delivers Clinically Superior CGM Metrics
Higher C-peptide linked to transformative CGM improvements: time below range dropped from 2% (<50 pmol/L) to 1% (101-200 pmol/L); glucose variability fell from 37.5% CV to 32.5%; time in range rose from 45% to 55%; time above 13.9 mmol/L halved from 20% to 10%. All pairwise comparisons reached p<0.05 significance, with no differences below 10 pmol/L and between 10 and 49 pmol/L.
C-Peptide ≥100 pmol/L Doubles Odds of Glycemic Success
C-peptide ≥100 pmol/L independently boosted odds of time below range <4% (OR 5.4, p<0.001) and was associated with HbA1c <53 mmol/mol (7%) (OR 1.8, p=0.043). These thresholds mark clinically meaningful gains, supporting beta cell preservation strategies and positioning routine C-peptide testing as a therapy individualization tool in everyday type 1 diabetes care.