Serum C-Peptide

Specimen Required

3-5cc Clotted Blood or Serum

Fasting Required

Purpose of the Test

To monitor insulin production by the beta cells in the pancreas and to help determine the cause of hypoglycaemia (low blood sugar) or assessment of insulin resistance (which can help diagnose the type of diabetes mellitus a person has or the severity of the metabolic syndrome).

When this test is required

C-peptide may be requested if you have newly diagnosed diabetes, as part of an evaluation of your “residual beta cell function” (how much insulin your beta cells are making) and to help differentiate the type of diabetes. The test may be requested if your doctor wants to monitor how your beta cells are performing and producing insulin over time and to determine if/when insulin injections may be required. C-peptide may be measured when there is sudden or recurring hypoglycaemia. Symptoms include sweating, palpitations, hunger, confusion, visual problems and seizures, although these symptoms also can occur with other conditions. The C-peptide test may be used in these circumstances to help determine the source of excess insulin, i.e. whether it is being produced in your body or coming from excessive injection of insulin.If you have had your pancreas removed or are one of the few patients to have had a pancreas transplant (in order to restore your ability to make insulin), your C-peptide concentration may be monitored to verify the effectiveness of treatment and the continued success of the procedure. Also it can be used to assess your response to weight loss after bariatric surgery.

What the Test Detects

This test measures the amount of C-peptide in a blood or urine sample. C-peptide and the hormone insulin are created from a larger molecule called proinsulin, and stored in the beta cells of the pancreas. When insulin is released into the bloodstream to help transport glucose into the body’s cells (to be used for energy), equal amounts of C-peptide also are released. This makes C-peptide useful as a marker of insulin production and indeed better in some cases than insulin as it is more stable in the blood (insulin immediately binding to receptors and therefore the concentration in the blood rapidly falling).C-peptide can be used to help evaluate the production of endogenous insulin (insulin made by the body’s beta cells) and to help differentiate it from exogenous insulin (insulin that is not produced by the body, e.g. injected insulin). This differentiation can be used to help diagnose and monitor a variety of conditions.See MoreSee Less

Preparation for the Test

Fasting for 8 to 10 hours before blood testing may be required, alternatively a meal stimulus or symptoms present thought to be due to hypoglycaemia.

Sample Requirements

A blood sample taken from a vein in your arm and sometimes a 24-hour urine sample is taken, or urine sample 2 hours after your largest meal of the day is taken.

Additional Notes

Even though they are produced at the same rate, C-peptide and insulin leave the body by different routes. Insulin is processed and eliminated mainly 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 5 times as much C-peptide in the bloodstream as insulin. If a person’s liver and kidneys are not clearing insulin and C-peptide efficiently then this can make results of the C-peptide test difficult to interpret. Therefore the test can give your doctor important information about your beta cells and insulin production, but it is not perfect.You will need to fast before a C-peptide blood test if the results will be used to evaluate hypoglycaemia. Alternatively, an appropriate blood sample taken during a hypoglycaemic episode may suffice. A meal stimulus is usually necessary for a urine test.

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