• C-peptide is released into your bloodstream when your pancreas makes insulin.
• Insulin is needed by your body to allow the glucose in your blood to enter your body’s cells to be used as energy. In doing this, insulin regulates your blood glucose and keeps it at the right level.
• Although C-peptide is not needed to regulate glucose, it stays in the body longer than insulin. Because it is in your blood longer, measuring C-peptide is a more reliable way of assessing how much insulin your pancreas is making than measuring insulin alone.
• Measuring C-peptide can also tell the difference between the insulin your body is making and any insulin you are taking by injections. (Injected insulin does not make C-peptide.)

Your pancreas releases C-peptide into the bloodstream as a byproduct when it makes insulin. The same amounts of insulin and C-peptide are released into your bloodstream at the same time. C-peptide doesn't make any difference to your blood glucose levels, but it stays in your blood longer than insulin. Because it is in your blood longer, measuring C-peptide is a more reliable way of finding out how much insulin your pancreas is making than measuring insulin alone.

All parts of the body need energy to work. Our main source of energy is glucose. Our body makes glucose from the food we eat and drink. Food molecules are broken down into sugars and absorbed in the small intestine then converted into glucose in the liver and circulated in the blood throughout the body.

To be able to use glucose, your body needs insulin. It enables the glucose in your blood to enter your body’s cells as it is needed.

Many of the body’s cells have insulin receptors on their surfaces. When insulin docks on to these receptors, signals are sent inside the cell, and this allows glucose to enter the cells.

If you have diabetes, the glucose - insulin system does not work as it should.

People with type 1 diabetes produce very little or no insulin and they must take insulin to control their blood glucose.

In type 2 diabetes, the insulin you are making isn’t being taken up by your cells properly and your cells are not responding effectively to the insulin signal. This is a condition called insulin resistance. When glucose can't get into your cells, your blood glucose levels rise. The pancreas tries to compensate by producing more and more insulin.

Over time, this strains the pancreas. Insulin is made by unique cells in your pancreas called beta cells in an area called the islets of Langerhans. These cells become damaged and cannot make enough insulin. Eventually, you may need insulin injections.

Measuring C-peptide levels can show how well your pancreas is making insulin.

It can be used to see if you have type 1 or type 2 diabetes.

• In type 1 diabetes, C-peptide levels are usually low because the pancreas produces little to no insulin.
• In type 2 diabetes, C-peptide levels are normal or high because the body is still producing insulin, but it is not working effectively.

Insulinomas: High C-peptide levels can also be due to insulinomas, which are rare tumours in the pancreas that can produce uncontrolled amounts of insulin and C-peptide. They are almost always benign (not cancer) and can usually be removed with surgery.

Low blood glucose (hypoglycaemia): Measuring C-peptide levels can help decide if this is due to high amounts of insulin being made or other causes.

Treatment monitoring: Measuring C-peptide levels is used to tell the difference between the insulin your body makes and the insulin you inject as treatment. The same amounts of C-peptide and insulin are made and released by your pancreas at the same time. If there is more insulin than C-peptide in your bloodstream, this is due to the injections of insulin you are taking.

Pancreatic transplant: If you have had your pancreas removed or have had a pancreas transplant to restore your ability to make insulin, your C-peptide levels may be monitored make sure this is working successfully.

Sample

Blood

Any preparation?

You will need to fast overnight.

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Even though they are produced at the same rate, C-peptide and insulin leave the body by different routes. Insulin is processed and removed by the liver, while C-peptide degrades and is removed by the kidneys. Since C-peptide remains in the body for much longer than insulin, normally there will be about five times as much C-peptide in the bloodstream as insulin.

If your liver and kidneys are not clearing insulin and C-peptide efficiently this can make results of the C-peptide test difficult to interpret. Although the C-peptide test gives important information about the state of your pancreas beta cells and insulin production, it is not perfect.

C-peptide testing may not be available in every laboratory. If a series of C-peptide tests are going to be performed they should be done by the same laboratory using the same method.

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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