Vitamin B-12 level

What the risks are:

Risks associated with venipuncture are slight:

• 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

Special considerations:

In testing for megaloblastic anemias of any sort, serum or red blood cell folate levels are usually also obtained.

Assay for blood levels of vitamin B12 has become much more accurate within the past few years because of improved testing abilities (a fewer number of false-normal values are obtained, only biologically active B12 is measured).

The cause of a vitamin B12 deficiency is usually determined by the Schilling test.

Hemolysis of the blood sample (rupture of some of the red blood cells) may affect test results.

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.