Insulin C-peptide is a blood test that measures the amount of C-peptide, a byproduct created when the hormone insulin is produced.

Blood is typically drawn from a vein, usually on the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The preparation for the test depends on the reason for the C-peptide measurement. Ask your health care provider if you should not eat (fast) prior to the test. The health care provider may advise you to stop taking 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 - 1 year)
• Toddler test or procedure preparation (1 - 3 years)
• Preschooler test or procedure preparation (3 - 6 years)
• School age test or procedure preparation (6 - 12 years)
• Adolescent test or procedure preparation (12 - 18 years)

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.