C-Peptide to Glucose Ratio
A practical index of β-cell insulin secretory function using C-peptide and glucose.
Last updated on: November 20, 2025
C-Peptide to Glucose Ratio Calculator
What is the C-Peptide to Glucose Ratio?
The C-peptide to glucose ratio (CGR) relates circulating C-peptide to plasma glucose and provides a practical estimate of β-cell insulin secretory capacity.
Because C-peptide is released in equimolar amounts with insulin and has a longer half-life, CGR is often more stable than insulin-based indices, especially in patients using exogenous insulin.
Why use the C-Peptide to Glucose Ratio?
- Helps distinguish insulin deficiency from insulin resistance phenotypes.
- Can be used even in patients on exogenous insulin, since C-peptide reflects endogenous secretion.
- Supports decisions about initiating or intensifying insulin therapy when interpreted in context.
How to interpret the C-peptide to glucose ratio
Insulin deficiency:
Low CGR, consistent with marked β-cell failure and insulin deficiency.
Impaired insulin secretion:
Intermediate CGR, suggesting reduced but still measurable β-cell function.
Preserved insulin secretion:
Higher CGR, indicating relatively preserved endogenous insulin production.
Clinical considerations and next steps
CGR should always be interpreted in clinical context including diabetes type, disease duration, renal function and concurrent therapies.
- Confirm fasting status or clearly document postprandial timing when interpreting results.
- Combine CGR with other markers such as HbA1c, autoantibodies and C-peptide alone to differentiate diabetes phenotypes.
- Very low CGR values may support early or intensive insulin therapy, particularly in suspected type 1 diabetes or LADA.
This page has been medically reviewed by Dr. Khoulah Attia – PharmD, Immunology Specialist.