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Blood Test: C-Peptide

Reviewed by: Larissa Hirsch, MD
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What Is a Blood Test?

By taking and testing a small sample of a person’s blood, doctors can check for many kinds of diseases and conditions. Blood tests help doctors check how the body’s organs are working and see if medical treatments are helpful.

To help your child get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test. If your child is anxious about it, work together on ways to stay calm.

What Is a C-Peptide Test?

C-peptide is made in the pancreas with insulin. Insulin is a hormone that controls the glucose level in the blood (blood sugar) by helping the glucose get into the cells. When insulin is released, so is C-peptide.

C-peptide doesn’t affect blood sugar. But measuring it helps doctors know how much insulin is being made because the pancreas typically releases equal amounts of C-peptide and insulin.

In general, high C-peptide levels mean the body is making a lot of insulin, while low C-peptide levels mean the body is making less insulin. Diabetes can cause the body to not make the right amount of insulin.

Why Are C-Peptide Tests Done?

Doctors do C-peptide tests to find out how much insulin the pancreas is making. This information can help them find out if someone has type 1 diabetes or type 2 diabetes. In type 1 diabetes, the pancreas makes little or no insulin and little or no C-peptide. In type 2 diabetes, C-peptide levels usually are normal or high, as the pancreas works harder to overcome insulin resistance by making more insulin.

C-peptide tests also can help find the cause of low blood sugar (hypoglycemia).

What if I Have Questions?

If you have questions about the C-peptide test or what the test results mean, talk to your doctor.

Reviewed by: Larissa Hirsch, MD
Date reviewed: September 2021