C Peptide Test for Diabetes
The C-peptide test helps your doctor identify whether you have type 1 diabetes (when the immune system attacks and destroys cells in the pancreas) or type 2 diabetes (when your body doesn't use insulin as well as it should). It shows how well your body makes insulin, which moves sugar (or “glucose”) from your blood into your cells.
Beta cells in your pancreas make insulin. During that process, these cells also release C-peptide.
C-peptide doesn't actually affect your blood sugar. But your doctor can measure its level to help them figure out how much insulin you’re making and decide whether you need to take insulin to control your condition.
Why Would I Get a C-Peptide Test?
Doctors don't use the C-peptide test to actually diagnose diabetes, but it can give them a reading to help treat it.
It can tell the difference between insulin your body has made and insulin that you took because only insulin your pancreas makes is associated with C-peptide.
You might get the C-peptide test:
- To find out whether you have type 1 or type 2 diabetes
- When you have type 1 diabetes and your doctor needs to know how much insulin your pancreas still makes
- To find out if it is time to start insulin in a patient with type 2 diabetes
- To find out why you have low blood sugar (hypoglycemia)
- To diagnose a tumor of the pancreas that releases insulin, called an insulinoma
- If you've had your pancreas removed
How to Prepare for C-Peptide Test
Your pancreas makes insulin and releases C-peptide when you eat. You might need to fast, or stop eating, 8 to 10 hours before the test. Sometimes, your doctor may want to stimulate your pancreas to measure how much C-peptide your body releases in response to food. So, the test is done after you eat.
Let your doctor know about any medicines you are on. Include medicines you take by prescription and those you buy over the counter, such as herbal supplements or vitamins.
C-peptide test cost
C-peptide test cost varies. Insurance will typically pay for the test, but you may have a copay or deductible. Follow up with your insurance company to learn what cost you’ll need to cover, if any.
If you don’t have health insurance and pay out of pocket, ask your doctor’s office or lab how much the test costs. The test may cost $74 - $111, depending on the lab.
How Is It Done?
A C-peptide test typically uses a sample of your blood.
To take a blood test, someone in your doctor’s office or a lab will collect your blood sample in a vial or syringe by putting a needle into your vein, usually in your forearm. You may feel a slight prick.
For a urine test, you will pee into a cup as instructed. For a 24-hour sample, you'll need to collect all the pee that you produce in a day.
C-peptide test at home
A C-peptide blood test can’t be done on your own at home. Your doctor may arrange for a health care professional to draw your blood at home if medical concerns make it hard to leave the house. Insurance may not cover all costs of a home blood draw.
If your doctor orders a C-peptide urine test, you can collect a urine sample at home and bring it to the lab.
C-Peptide Test Results
You should have your results in a few days. A normal C-peptide range is 0.5-2.0 nanograms per milliliter.
These levels can be high when your body makes more insulin than usual. Levels are low when your body makes less than it normally should.
A high level can mean that you:
- Have insulin resistance — meaning your body doesn't use it as well as it should (if you have type 2 diabetes, your insulin levels may be high)
- Have a tumor, called an insulinoma
- Have kidney disease
A high level may also show you take too much of a certain class of medicine to treat type 2 diabetes. They’re called sulfonylureas and include:
- Chlorpropamide (Diabinese)
- Glimepiride (Amaryl)
- Glipizide (Glucotrol, Glucotrol XL)
- Glyburide (DiaBeta, Glynase PresTab, Micronase)
- Tolazamide or tolbutamide
A low C-peptide level may mean that:
- You have type 1 or type 2 diabetes with a tired pancreas or more advanced disease.
- You are on insulin shots, and it is suppressing the release of insulin from your pancreas.
- You have low blood sugar , so your pancreas stops releasing insulin, or you're taking insulin so your pancreas isn't releasing any.
- Treatment has shrunk your insulinoma.
Ask your doctor for more details about what your test results mean. Then, find out what treatment steps you'll need to take.
Risks of a C-Peptide Test
A blood draw from your vein carries little risk. The size and location of your veins may make it easier or harder for a health care professional to draw your blood.
Blood draw risks include:
- Bleeding from the puncture site, especially if you take blood thinners
- Fainting or feeling lightheaded
- Hematoma, or bruising, at the blood draw site
- Infection, a slight risk when your skin is broken
Takeaways
A C-peptide test shows how much insulin your body makes and helps your doctor tell the difference between whether you have type 1 or type 2 diabetes. Your doctor will use the test results to figure out if and how much insulin you need to control your blood sugar levels. A C-peptide test is also used to help diagnose other medical conditions, such as Addison's disease or a tumor on your pancreas. Talk with your doctor to learn more about what your test results mean and the steps you can take to stay healthy.
C-Peptide Test FAQs
What is a normal C-peptide level for type 2 diabetes?
Normal C-peptide levels range from 0.5 to 2.0 nanograms per milliliter. A value higher than 2.0 means you may have type 2 diabetes.
How do C-peptide levels differentiate between type 1 and 2 diabetes?
C-peptide is released when your pancreas produces insulin. People with type 2 diabetes make insulin but their bodies don’t use it properly. So their C-peptide levels are high. People with type 1 diabetes don’t release insulin properly in response to eating, so their C-peptide levels are low while their blood sugar levels are high.
Is C-peptide an inflammatory marker?
C-peptide shows how well your body makes insulin. Some research suggests that C-peptide levels may show high levels of inflammation, but more studies are needed. If you have signs of inflammation, your doctor may order a C-reactive protein (CRP) test.
What C-peptide level indicates diabetic ketoacidosis?
C-peptide is not associated with diabetic ketoacidosis (DKA). To diagnose DKA, doctors will check your blood sugar level, blood pH level, whether you have ketones in your blood or pee, and your blood bicarbonate level.
