This test measures how much insulin your body produces. If you have hypoglycemia, or low blood sugar, or other issues related to diabetes, your doctor may order a C-peptide test. This test is often done using a blood sample, but a urine sample can also be used.
If you have diabetes, it can be hard for a health care provider to tell how much insulin your pancreas produces by just looking at your physical symptoms. A C-peptide test measures the amount of insulin your body makes.
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 doctor may also recommend other diabetes-related tests.
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 health care 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's inability to make insulin.
This number is just one factor your doctor 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.
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 health care provider's office. Your health care 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.
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.
Your diet, including when you last ate, can influence your C-peptide levels.
Sometimes the test is done after fasting, and other times it is done after you eat a meal. Your health care provider will give you instructions on how the test is to be done and, if needed, how to collect a urine sample.