A blood test is a way for doctors to get a sample of your body’s blood and look for different conditions. The C peptide test helps determine the level of insulin being produced by your pancreas. It’s used to help differentiate between type 1 and type 2 diabetes, to monitor your diabetes, and to check for problems such as an insulinoma (tumor of the pancreatic islet cells). You may also be asked for a urine test.
Your doctor will ask you to fast for the test and to not take any medication that might affect the results. Then, they will use a needle to take a small sample of your blood. You might feel a slight sting when the needle goes in. The sample is then sent to a lab for testing. The test can also be conducted with a urine sample, though this is less common.
Normal levels of c peptide are 0.9 to 1.8 ng/ml. A low c peptide result could indicate that your body is not producing enough insulin, which happens in type 1 diabetes and in advanced type 2 diabetes. It can also be a sign of a tumor in the pancreas, or of insulin resistance from obesity.
The c peptide test is used to help classify type 1 and type 2 diabetes, but it must be interpreted in the context of your medical history and family history. It can also be useful in determining whether you have MODY, but this should only be done three to five years after diagnosis.