C-Peptide Blood Test

What Is a C-Peptide Blood Test and Why Is It Done?

A C-peptide test helps show how much insulin (a kind of hormone) the pancreas is making. Doctors might order the test to find out:

• if someone has type 1 diabetes or type 2 diabetes
• how well diabetes treatments are working
• the cause of low blood sugar, or hypoglycemia (hi-poe-gly-SEE-me-uh)

What Is C-Peptide?

C-peptide, which is short for connecting peptide, is a substance that’s made in the pancreas along with insulin. Insulin controls the level of glucose (a sugar that comes from food) in the blood 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 C-peptide helps doctors know how much insulin the body is making. The pancreas typically releases equal amounts of C-peptide and insulin.

Top Things to Know

• The C-peptide blood test checks the level of a substance called C-peptide in the blood.
• Doctors may order it to help find out what someone’s insulin level is.
• Kids might need to stop taking certain medicines or not eat or drink before the blood test.
• Your doctor can explain what it means if C-peptide levels are too low or too high.

How Can I Help My Child Prepare for a Blood Test?

To help kids 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 nervous about it, work together on ways to stay calm. Deep breathing or even imagining being in a place that makes your child feel safe and relaxed can help.

What Do C-Peptide Test Results Mean?

Your doctor will explain what the results of the C-peptide test mean for your child. What’s “normal” varies based on things like age and gender.

In general, low C-peptide levels mean the body is making less insulin, while high C-peptide levels mean the body is making a lot of insulin.

Diabetes

Diabetes can cause the body to not make the right amount of insulin.

• With type 1 diabetes, the pancreas makes little or no insulin and little or no C-peptide.
• With type 2 diabetes, insulin and C-peptide levels are usually normal or high.

Low C-Peptide Level

A low level of C-peptide could also be due to problems with the liver or adrenal glands or a diabetes treatment plan that isn’t helping enough.

High C-Peptide Level

Sometimes C-peptide might be high because of a condition where the body makes too much insulin, like:

• a pancreas or kidney problem
• Cushing syndrome (too much of the hormone cortisol in the body)
• too little potassium
• insulin resistance (when the body doesn't respond to insulin as it should)

What Else Should I Know?

When kids have a C-peptide blood test, they may have an insulin blood test too.

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