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Vitamin B12 level

• Overview
• Risks
• Results

Definition:

The vitamin B12 level is a test to tell how much vitamin B12 is in your blood.

How the test is performed:

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. The band is removed to let the blood flow again. Once the blood has been collected, the needle is removed. The puncture site is covered to stop any bleeding.

In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a small blade (lancet). The blood may be collected in a small glass tube (pipette), on a slide, onto a test strip, or into a small container. A bandage may be placed on the puncture site if there is any bleeding.

How to prepare for the test:

You should not eat or drink for about 6 - 8 hours before the test. Tell your health care provider if you are taking any medicines that may affect test results, including colchicine, neomycin (Neosporin), para-aminosalicylic acid, and phenytoin (Dilantin).

How the test will feel:

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

Why the test is performed:

This test is most often done when other tests (which may include CBC , RBC indices, reticulocyte count , blood smear, or others) suggest a blood disorder called megaloblastic anemia .

Pernicious anemia is the megaloblastic anemia caused by poor vitamin B12 absorption. This can occur when the stomach makes less intrinsic factor, a substance needed for vitamin B12 absorption. This test may also be done to find the cause of nervous system problems.

References:

Goldman L, Ausiello D. Cecil Textbook of Medicine . 22nd ed. Philadelphia, Pa: Saunders, 2003.

Hoffman R, Benz E, Shattil S, Furie B, Cohen H. Hematology: Basic Principles and Practice . 4th ed. Philadelphia, Pa: Churchill Livingstone, 2004.

• Review Date: 3/13/2007
• Reviewed By: Mark Levin, M.D., Hematologist and Oncologist, Newark, NJ. Review provided by VeriMed Healthcare Network.

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