Insulin C-peptide

How the Test is Performed:
Adult or child:
Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding .

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:
Fast for 8 hours before the test.
The health care provider may advise you to withhold medications that can interfere with test results, including injected insulin and/or oral antidiabetic medications.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:



How it Feels:
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 .

Risks:

  • excessive 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



Why this Test is Performed:
C-peptide is measured to differentiate endogenous (produced by the body) from exogenous (injected into the body) insulin in patients who require insulin but may also have some residual endogenous production.

When insulin is initially synthesized by the beta cells of the pancreas, it is produced as a large molecule (propeptide). This molecule is then cleaved at 2 sites and the distal segments are attached together by 2 "disulfide" bonds. The intermediate segment (C-peptide) is released at the same time insulin is released but has no known function.

Normal Values:
0.5 to 3.0 ng/ml

Note: mg/ml = nanograms per milliliter

Abnormal Results:
Normal values in a patient requiring insulin injections indicates that the person's body is still producing some insulin.

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

Additional conditions under which the test may be performed:



Cost:
The estimated cost is $40.

Special Considerations:
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.