Does this test have other names?
Connecting peptide insulin, insulin C-peptide, proinsulin C-peptide
What is this test?
This urine test looks at how well your body makes the hormone insulin. It's used to help diagnose blood sugar disorders.
Your body needs insulin to move sugar from your bloodstream into your cells for energy. A healthy pancreas makes equal amounts of insulin and the protein C-peptide. By measuring C-peptide, your healthcare provider can also learn about your insulin level. This test is often done using a blood sample, but a urine sample can also be used.
Why do I need this test?
Measuring C-peptide can show if you have type 1 or type 2 diabetes. With type 1 diabetes, your body doesn't make any insulin. With type 2 diabetes, either your body doesn't make enough insulin or your cells can’t use it normally.
If you have diabetes, the C-peptide test can show how well your treatment is working.
The C-peptide test may also be done to find the cause of low blood sugar. Or it may be done to check the activity of tumors that make insulin.
What other tests might I have along with this test?
Your healthcare provider may also want you to have tests such as:
Blood glucose test. This measures the amount of sugar (glucose) in your blood.
Glucagon test. This measures the level of another hormone made by the pancreas. Glucagon can increase blood sugar.
A1C test. This is also known as glycosylated hemoglobin blood test. This is a measure of your blood glucose levels over the past 3 months. It shows how well your blood sugar is controlled.
Insulin assay. This test measures your insulin level.
What do my test results mean?
Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. In urine, the C-peptide level is measured in picomoles per liter (pmol/L). A normal C-peptide test result is less than 200 pmol/L. The results may vary depending on the lab used for testing.
A high level of C-peptide may mean you need to adjust the amount of insulin you take. Or it may mean you have a kidney problem. Or you may have an insulinoma. This is a tumor that grows in the cells in the pancreas that make insulin.
A level of C-peptide that's lower than normal means that your body isn't making enough insulin. Or it means that your pancreas isn't working normally.
How is this test done?
This test is done with a urine sample. You’ll collect your urine in a plastic cup with a lid. You may do this at home or at the healthcare provider's office. Your healthcare provider will tell you how and when to collect the sample.
Does this test pose any risks?
This urine test has no health risks.
What might affect my test results?
Taking insulin for your diabetes can raise your C-peptide level. Your C-peptide level can also change if your kidneys aren't working normally. The time of your most recent meal may affect your C-peptide level.
How do I get ready for this test?
The urine test is usually done after you eat a meal. Ask your healthcare provider for instructions. Tell your healthcare provider about all medicines, vitamins, supplements, and herbs you are taking. This includes medicines that don't need a prescription. Also tell your healthcare provider about any illegal drugs you use.
June 20, 2018
Goldman's Cecil Medicine. Goldman L. 2015;25:1548-55., Urine C-Peptide Creatinine Ratio Is a Noninvasive Alternative to the Mixed-Meal Tolerance Test in Children and Adults With Type 1 Diabetes. Besser R, et al. Diabetes Care. 2011 March;34(3):607-9.
Haldeman-Englert, Chad, MD,Sather, Rita, RN