The C peptide assay is a tool used by doctors to monitor and treat diabetes. It shows how well the body produces insulin, which is responsible for moving sugar (or glucose) from the blood to the cells.
This measurement helps your doctor decide if you need to take insulin to manage your condition, and if you are already taking insulin, it can be used to verify that the dose is appropriate.
Doctors can use this test whether they have type 1 diabetes where the immune system attacks and destroys cells in the pancreas, or type 2 diabetes where the body is unable to use insulin fully.
Where do C-peptides come from?
The peptides in the pancreas are the most common peptides.
The beta cells in the pancreas produce insulin. During this process, these cells also release C peptide.
This substance does not actually affect blood sugar. But your doctor can measure its levels to help understand how much insulin your body is producing.
Why do I need this test?
Doctors don’t use this test to diagnose diabetes, but the readings help them adjust their diabetes treatment. It can tell the difference between the insulin your body produces and the insulin you take.
A C-peptide measurement may be needed if:
- To find out if you have type 1 or type 2 diabetes.
- In the case of type 1 diabetes, the doctor needs to know how much insulin the pancreas is still producing.
- In type 2 diabetes, your doctor will need to determine how much insulin you are producing or if you need to start taking insulin.
- Understand why hypoglycemia (low blood sugar) occurs.
- Diagnose a pancreatic (insulin-releasing) tumor, also called an insulinoma.
- If the pancreas has been removed.
What is the preparation for C-peptide assay?
Fasting may be required 8 to 10 hours before the test.
Fasting may be required 8 to 10 hours prior to the test. In some cases, the test will be done after eating.
Let your doctor know about any medications you take, including those taken as prescribed and over-the-counter medications such as herbal supplements or vitamin supplements.
How is the C-peptide assay performed?
The C-peptide assay requires the use of a blood or urine sample.
To perform the blood test, the nurse sticks a needle into a vein, usually in the forearm. A little stinging may be felt. The blood is collected into a vial or syringe.
For a urine test, the urine is drained into a designated urine cup as directed. If a 24-hour sample is to be measured, a full day of urine will be collected.
How do I interpret the results?
The results will be available in a few days. The normal range for C-peptide is 0.5 to 2.0 nanograms per milliliter.
C-peptide levels may be extremely high when the body is producing more insulin than usual. When the body produces less insulin than normal, C-peptide levels may be extremely low.
High levels of C-peptide indicate:
- There is insulin resistance, meaning that the body is not using insulin well.
- There is a tumor, called an insulinoma.
- Have kidney disease.
High levels of C-peptide may also indicate an overdose of a certain type of medication when treating type 2 diabetes. They are called sulfonylureas and include:
- Chlorosulfonylurea;
- Glimepiride;
- Glipizide;
- Glibenclamide;
- Tolazamide or toluenesulfonylurea.
Low levels of C peptide may indicate:
- Have type 1 or type 2 diabetes.
- The pancreas is not working as it should, or insulin production is decreased because insulin is being used to treat diabetes.
- Extremely low blood glucose levels.
- Treatment has shrunk the insulinoma.
Ask your doctor for more detailed information related to the measurement results. In addition, determine what treatment is needed.