Vitamin B-12 level

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The vitamin B-12 level is a test to determine the level of vitamin B-12 in the blood.

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. 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.

In infants or young children:

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. A bandage may be applied to the puncture site if there is any bleeding.

Fast for 6 - 8 hours before the test. Consult with the health care provider if you are using medications that may affect test results, including colchicine, neomycin, para-aminosalicylic acid, and phenytoin.

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.

This test is most often performed when other tests (which may include CBC, RBC indices, reticulocyte count, blood smear, or others) indicate the presence of a megaloblastic anemia.

Pernicious anemia is the megaloblastic anemia caused by poor absorption of vitamin B-12. This is usually caused by decreased production of intrinsic factor, a substance essential to vitamin B-12 absorption, in the stomach. This test may also be performed as part of the testing to determine the cause of nervous system disorders.

Review Date: 02/04/2005
Reviewed By: Rita Nanda, M.D., Department of Hematology/Oncology, University of Chicago Medical Center, Chicago, IL. Review provided by VeriMed Healthcare Network.