MedlinePlus Medical Encyclopedia: Insulin C-peptide

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Insulin C-peptide

Contents of this page:
Alternative names Definition How the test is performed How to prepare for the test How the test will feel	Why the test is performed Normal Values What abnormal results mean What the risks are Special considerations

Alternative names

C-peptide

Definition Return to top

This is a blood test that measures the amount of C-peptide, a subunit of the hormone insulin.

How the test is performed Return to top

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. After the blood is collected, the band is removed to restore circulation. Then, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test Return to top

The preparation for the test depends on the reason for the c-peptide measurement. Ask your health care provider if you should fast prior to the test. The health care provider may advise you to withhold medications that can interfere with test results.

For infants and children:
The preparation you can provide for this test depends on your child's age and experience. For specific information regarding how you can prepare your child, see the following topics:

infant test or procedure preparation (birth to 1 year)
toddler test or procedure preparation (1 to 3 years)
preschooler test or procedure preparation (3 to 6 years)
schoolage test or procedure preparation (6 to 12 years)
adolescent test or procedure preparation (12 to 18 years)

How the test will feel Return to top

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed Return to top

C-peptide is measured to differentiate insulin produced by the body from insulin injected into the body. When insulin is synthesized by the beta cells of the pancreas, it is produced as a large molecule (a propeptide). This molecule is then split into two pieces: insulin and C-peptide. The function of C-peptide is not known.

The C-peptide level may be measured in a patient with type II diabetes to see if any insulin is still being produced by the body. It may also be measured in the evaluation of hypoglycemia (low blood sugar) to see if the person's body is producing too much insulin.

Normal Values Return to top

0.5 to 2.0 ng/ml (nanograms per milliliter)

What abnormal results mean Return to top

Normal values in a patient requiring insulin injections indicates that the person's body is still producing some insulin. Normal values in a patient who has low blood sugar indicates that the patient is making too much insulin.

Low values (or no Insulin C-peptide) indicates that the person's pancreas is producing little or no insulin.

What the risks are Return to top

The risks associated with having blood drawn are:

bleeding
fainting or feeling lightheaded
hematoma (blood accumulating under the skin)
infection (a slight risk any time the skin is broken)
multiple punctures to locate veins

Special considerations Return to top

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Update Date: 1/27/2004

Updated by: Todd T. Brown, M.D., Division of Endocrinology and Metabolism, Johns Hopkins Hospital, Baltimore, MD. Review provided by VeriMed Healthcare Network.

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