Does this test have other names?
What is this test?
This test measures how much insulin your body makes. If you have low blood sugar (hypoglycemia) or other problems related to diabetes, your healthcare provider may order a C-peptide test. This test is often done using a blood sample, but a urine sample can also be used.
Why do I need this test?
If you have diabetes, it can be hard for a healthcare provider to tell how much insulin your pancreas makes by just looking at your physical symptoms. A C-peptide test measures the amount of insulin your body makes.
What other tests might I have along with this test?
C-peptide can be measured with either a blood test or a urine test. Sometimes the ratio of urine C-peptide to creatinine is used to help measure how much insulin your body makes. Your healthcare provider may also recommend other diabetes-related tests.
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.
C-peptide levels are measured in picomoles per liter (pmol/L). A normal C-peptide test result is less than 200 pmol/L. Higher levels of C-peptide typically mean higher levels of blood sugar. They may also mean that you are making too much insulin because you have a tumor called an insulinoma. Lower levels of C-peptide mean lower levels of blood sugar or your body cannot make insulin.
The results are just one thing your provider uses to check your overall health. The ratios of many different components, including C-peptide, are important for finding out the best way to treat your diabetes.
How is this test done?
A C-peptide test can be done with either a blood or urine sample. For the urine test, you can provide the sample at home or at a healthcare provider's office. Your healthcare provider will give you instructions on how and when to give the sample.
When a blood sample is needed, it is drawn by putting a needle into a vein in your arm or hand.
Does this test pose any risks?
If a urine sample is used, it poses no risks.
Taking a blood sample with a needle carries small risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
Your diet, including when you last ate, can affect your C-peptide levels.
How do I get ready for this test?
Sometimes the test is done after fasting, and other times it is done after you eat a meal. Your healthcare provider will give you instructions on how the test is to be done and how to collect a urine sample, if needed.