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C-Peptide Test: normal range & what your result means
Written & medically reviewed by Dr. Sanjay Anbu, MBBS · Last reviewed
Medically reviewedC-peptide is released in equal amounts with the body’s own insulin. Measuring it shows how much insulin your pancreas is still making — useful in telling diabetes types apart.
About the test
Why the C-peptide test is done
- Distinguishing type 1 from type 2 diabetes
- Checking how much insulin the pancreas still makes in long-standing diabetes
- Investigating repeated low blood sugar
Reference range
Typical adult range
| Measure | Typical adult range |
|---|---|
| Typical fasting | About 0.5–2.0 ng/mL |
| Unit note | Some labs report nmol/L (about 0.17–0.66) |
Typical adult range; labs differ — use the range on your report. Ranges also vary with age, sex, pregnancy and the method used. Your doctor interprets the result alongside your symptoms and history.
Results
What a HIGH result can mean
- Insulin resistance, as in type 2 diabetes, obesity or PCOS
- Kidney disease (C-peptide is cleared by the kidneys)
- Rarely, an insulin-producing tumour
Results
What a LOW result can mean
- Type 1 diabetes — the pancreas makes little insulin
- Long-standing type 2 diabetes with reduced insulin production
- Low blood sugar from injected insulin (C-peptide stays low)
Preparation
Before the test
- Usually fasting; sometimes taken with a blood sugar sample
- Tell the lab about diabetes medicines and insulin
Red flags
When to get urgent help
- Low sugar symptoms — shakiness, sweating, confusion — take sugar if you can and seek help
- Very high sugar with vomiting or drowsiness — seek urgent care
Explore more
Related pages
References
Sources & further reading
Frequently asked questions
What does low C-peptide mean?
It means the pancreas is making little insulin, as in type 1 diabetes or advanced type 2 diabetes.
Why test C-peptide instead of insulin?
C-peptide lasts longer in the blood and is not affected by injected insulin, so it better reflects your own insulin production.
Does C-peptide decide if I need insulin?
It is one piece of information. Your doctor considers it together with your sugar levels, symptoms and other tests.