Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is first 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 drawn, 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.

Consult the health care provider if you are using drugs that can interfere with test results. Drugs that can increase gastrin measurements include antacids, H2-blocking agents (such as cimetidine), and proton pump inhibitors (such as omeprazole).

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)

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 may be ordered when disorders associated with abnormal gastrin production are suspected. Too much gastrin causes severe peptic ulcer �disease.

Gastrin is a hormone produced by specialized cells in the stomach. When there is food in the stomach, gastrin is secreted into the blood. Gastrin in the bloodstream stimulates cells in the stomach to secrete acid. Small amounts of gastrin may also be produced by the pancreas and possibly the intestines. As stomach and intestinal acidity rises, gastrin production normally decreases.

Zollinger-Ellison syndrome is a gastrin-producing tumor which may be present in the stomach or pancreas. G-cell hyperplasia is an overactivity of the gastrin-producing cells of the stomach.

Less than 100 pg/ml (picograms per milliliter)

Greater-than-normal levels may indicate:

• use of antiacids or other acid-suppressive medications
• chronic atrophic gastritis
• G-cell hyperplasia (overactivity of gastrin-producing cells in the stomach)
• Zollinger-Ellison syndrome

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

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.