10/23/2026
C-peptide is a small chain of amino acids released in equal amounts with insulin when the pancreas produces it. Because injected or pump-delivered insulin does not contain C-peptide, a blood test can estimate how much insulin your body is still making—even if you currently use insulin.
Why does this matter? Very low or undetectable C-peptide generally indicates that the pancreas produces little or no insulin. This is typical of established type 1 diabetes but may also occur in long-standing type 2 diabetes and other insulin-deficient conditions. Higher levels indicate continued insulin production and may suggest insulin resistance, as commonly occurs in type 2 diabetes.
C-peptide testing can help clarify diabetes type, particularly in adult-onset or atypical cases. It may also guide treatment decisions and is used in research to measure preservation of insulin-producing beta cells. However, C-peptide cannot determine diabetes type by itself.
The test is often performed with a glucose measurement because glucose levels affect how much insulin the pancreas releases. Kidney function, whether you were fasting and certain medications may also influence the result.
Not everyone with diabetes needs C-peptide testing. If your diagnosis is uncertain, treatment results are unexpected or insulin needs change significantly, ask your healthcare provider whether testing could provide useful information for your individualized care.
