Vasoactive intestinal polypeptide (VIP) is a substance found throughout the body, but the highest levels normally occur in the nervous system and gut. VIP has many functions:

• It helps control or send nerve signals
• It helps relax certain muscles along the gastrointestinal tract
• It increases the amount of water and electrolytes released from the pancreas and gut
• It triggers the release of hormones from the pancreas, gut, and hypothalamus
• It helps breakdown fat and glycogen
• It stimulates bile flow
• It blocks gastrin and gastric acid secretion

A blood test can be done to find out how much VIP you have in your blood.

Blood is drawn from a vein, usually 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. During the procedure, the band 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.

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.

You should not eat or drink anything for 4 hours before the test.

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.

This test is used to confirm the presence of a VIPoma, a tumor that releases VIP.

Less than 75 pg/ml (picograms per milliliter) is normal.

A higher-than-normal level may be a sign of a VIPoma.

The risks associated with having blood drawn are slight:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

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.

Hadley ME, Levine JE. Endocrinology. 6th ed. Upper Saddle River, NJ: Pearson Prentice Hall, 2007:220-221.