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Home > Patient & Family Resources > Health Library > C-Peptide Test
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A C-peptide test measures the level of this peptide in the blood. It is generally found in amounts equal to insulin. This is because insulin and C-peptide are linked when first made by the pancreas. Insulin helps the body use and control the amount of sugar (glucose) in the blood. Insulin allows glucose to enter body cells where it is used for energy. The level of C-peptide in the blood can show how much insulin is being made by the pancreas. C-peptide does not affect the blood sugar level in the body.
A C-peptide test can be done when it is not clear whether type 1 diabetes or type 2 diabetes is present. A person whose pancreas does not make any insulin (type 1 diabetes) has a low level of insulin and C-peptide. A person with type 2 diabetes can have a normal or high level of C-peptide.
A C-peptide test can also help find the cause of low blood sugar (hypoglycemia). Possible causes of low blood sugar are excessive use of medicine to treat diabetes or a noncancerous growth (tumor) in the pancreas (insulinoma). Because man-made (synthetic) insulin does not have C-peptide, a person with a low blood sugar level from taking too much insulin will have a low C-peptide level but a high level of insulin. An insulinoma causes the pancreas to release too much insulin, which causes blood sugar levels to drop (hypoglycemia). A person with an insulinoma will have a high level of C-peptide in the blood when they have a high level of insulin.
A C-peptide test is done to:
Your doctor will give you instructions about eating and drinking before this test.
Insulin and some oral medicines used to treat type 2 diabetes can change the test results. Your doctor may ask you to stop these medicines before your blood test.
A health professional uses a needle to take a blood sample, usually from the arm.
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
Current as of:
March 31, 2020
Author: Healthwise StaffMedical Review: E. Gregory Thompson MD - Internal MedicineKathleen Romito MD - Family MedicineAlan C. Dalkin MD - Endocrinology
Current as of: March 31, 2020
Author: Healthwise Staff
Medical Review:E. Gregory Thompson MD - Internal Medicine & Kathleen Romito MD - Family Medicine & Alan C. Dalkin MD - Endocrinology
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