C-Peptide Test
Reviewed
Also called: insulin C-peptide, connecting peptide insulin, proinsulin C-peptide
This test measures the level of C-peptide in a sample of your blood or urine (pee).
Specimen: blood or urine
Why this test may be ordered
- To find the cause of hypoglycemia (low blood glucose) that may be linked to high insulin levels.
- To help manage diabetes treatment by showing how much insulin your pancreas is making.
- To monitor treatment for a rare pancreatic tumor (insulinoma) that makes too much insulin.
- To help determine whether you have type 1 or type 2 diabetes when the diagnosis is uncertain.
Preparation and collection
For a C-peptide blood test, you may need to fast (not eat or drink) for 8-12 hours before the test. Your provider may also want to test C-peptide after you've eaten something. Ask your provider if there are any specific instructions you need to follow before either a blood or a urine test.
A C-peptide test usually uses a sample of your blood. But the test may also be done on a sample of all your urine collected over a 24-hour period. During a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. There are no known risks to a urine test.
Understanding results
The meaning of your results depends on your age, health, the medicines you take, and the results of other tests, such as a blood glucose test.
- High C-peptide level: A high level of C-peptide usually means that your body is making too much insulin. Limitation: A C-peptide test is not used to diagnose diabetes. Next step: Other tests, such as blood glucose and urine glucose, are used to screen for and diagnose diabetes.
- Low C-peptide level: A low level of C-peptide may mean your body isn't making enough insulin. Limitation: The meaning of your results depends on your age, health, the medicines you take, and the results of other tests, such as a blood glucose test. Next step: If you have questions about your results, talk with your provider.
- Decrease after treatment for an insulin-producing tumor: If you have been treated for an insulin-producing tumor in your pancreas, a decrease in your C-peptide levels means your treatment is working. Limitation: The meaning of your results depends on your age, health, the medicines you take, and the results of other tests, such as a blood glucose test. Next step: If you have questions about your results, talk with your provider.
- Increase after treatment for an insulin-producing tumor: An increase in your C-peptide may mean that your tumor is back. Limitation: The meaning of your results depends on your age, health, the medicines you take, and the results of other tests, such as a blood glucose test. Next step: If you have questions about your results, talk with your provider.
- A C-peptide test is not used to diagnose diabetes. Other tests, such as blood glucose and urine glucose, are used to screen for and diagnose diabetes.
- Results must be interpreted by a healthcare professional based on your age, health, medicines, and other test results.
What to do next
If you have questions about your results, talk with your provider.
- What do my C-peptide test results mean for my health?
- Do I need any other tests based on these results?
- How will these results affect my diabetes treatment plan?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.