C peptide is a substance made by the pancreas that’s linked to insulin, and it helps control the amount of sugar in the blood. Doctors can measure c peptide levels to help figure out how much insulin someone is making. The test can also tell if someone has type 1 or Type 2 diabetes, and it can show how well diabetes treatment is working.
A c peptide test can be done by blood or urine. For the blood test, you will need to fast (avoid food and drink other than water) for eight to 12 hours before the procedure. You may need to stop certain medications before the test as well. Your healthcare provider will provide you with specific instructions.
The c peptide test does not have any risks. A blood sample is usually taken in a doctor’s office or lab. A needle will be inserted into your arm or hand, and you will feel a slight sting. The sample will be put into a tube to be tested.
C peptide levels can vary from day to day, but are typically between 0.5 and 2.0 nanograms per milliliter of blood (or 0.17 and 0.83 nanomoles per liter of urine) in healthy people. If the results are low, it can be a sign of type 1 or Type 2 diabetes (especially when it’s combined with a low blood glucose level), insulin resistance, or a condition called addison disease in which the adrenal glands don’t produce enough hormones including cortisol and aldosterone.