About Our C-Peptide Test
Purpose of the test
The purpose of a C-peptide test is to evaluate how much insulin your body is producing. This information can help your health care provider understand how well the pancreas is functioning and whether your body is making enough insulin.
C-peptide testing may be used in reaching a diagnosis or for monitoring in several situations:
- Evaluating hypoglycemia: The test can help determine the cause of low blood sugar, such as whether it’s related to excess insulin production or insulin use. Low levels of C-peptide are also seen in Addison disease and liver disease.
- Guiding diabetes treatment: C-peptide levels can help assess how much insulin your body is still making, which may inform treatment decisions (i.e., if one needs an insulin injections/pump if too low).
- Clarifying diabetes type: In some cases, the test may help distinguish between type 1 and type 2 diabetes when the diagnosis is uncertain.
- Monitoring pancreatic conditions: The test may be used to help detect or monitor conditions such as insulinoma (pancreatic tumor) or other disorders affecting insulin production.
- Elevated C-peptide values may be present in Cushing syndrome, insulin resistance, decreased potassium level (hypokalemia), and kidney failure.
What does our C-peptide test measure?
A C-peptide test measures the level of C-peptide in a sample of blood or urine. C-peptide is produced by the pancreas when it makes insulin. When insulin is released into the bloodstream, C-peptide is released in equal amounts.
Because of this, the level of C-peptide reflects how much insulin your body is producing. This can help distinguish between insulin made by the body and insulin taken as medication.
Results are often considered alongside an insulin test and a glucose test to better understand how much insulin your body is making.
When should I get a C-peptide test?
C-peptide levels may be ordered when there is documented acute or recurring hypoglycemia and/or excess insulin is suspected. These tests help distinguish the body’s insulin from outside sources of insulin. Symptoms of hypoglycemia include:
- Sweating/chills
- Palpitations
- Hunger
- Nausea
- Headaches
- Confusion
- Blurred vision
- Dizziness/shaking/trembling
- Fatigue
- Fainting/coordination problems
- In severe cases, seizures and loss of consciousness
However, many of these symptoms can also occur with other conditions.
C-peptide testing may also be used in people with diabetes to help guide treatment. It can help determine whether the body is still producing insulin, which may influence whether insulin injections are needed or if other medications may be appropriate. In some cases, it’s ordered when the type of diabetes is uncertain.
Health care providers may also use a C-peptide test to monitor certain pancreatic conditions. For example, it may be ordered periodically in people diagnosed with insulinoma to evaluate treatment and check for tumor recurrence.
Less commonly, C-peptide levels may be monitored over time after pancreas removal or islet cell transplantation.
Finding a C-peptide Test
How to get tested
C-peptide testing is usually performed at a doctor’s office or another medical setting like a hospital or lab. The tests are normally ordered by a doctor but may be available without orders from your doctor at a walk-in lab.
Can I take the test at home?
In most cases, no. C-peptide tests are done in a medical setting. However, a provider may order urine collection that you complete at home and return to a lab.
How much does the test cost?
The cost of a C-peptide test will vary depending on factors such as where the test is done, and whether you have health insurance. When ordered by a doctor, insurance typically covers the test, although you may have to pay a copay or deductible. Your doctor’s office, lab, and health plan can provide information about any out-of-pocket costs that may be your responsibility.
Taking a C-peptide Test
C-peptide testing is usually done with a blood sample. In some cases, a urine sample may be collected instead. Your health care provider will give you specific instructions based on how the test is being used.
Before the test
How you prepare for a C-peptide test will depend on why the test is being ordered. You may be asked to fast for 8 to 12 hours before a blood test. In some cases, the test may be done after eating or after receiving a substance that stimulates insulin production. Be sure to carefully follow your provider’s instructions.
You may also be asked to avoid biotin-containing supplements before testing, since some supplements can interfere with certain lab assays.
During the test
For a blood test, a small sample of blood will be drawn from a vein in your arm using a needle and collected into a tube for testing. The procedure usually takes only a few minutes.
If a urine test is ordered, you may be asked to collect your urine over a 24-hour period. In testing for type 2 diabetes, a post-meal collection may be done 2 hours after the meal. Your provider will explain how to collect and store the sample.
After the test
There are no special restrictions after a C-peptide blood test, and you can usually return to your normal activities right away. If you had blood drawn, you may have mild soreness or bruising at the puncture site.