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A vitamin B12 test measures the amount of vitamin B12 in the blood.

The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

High values

• High levels of vitamin B12 can occur in liver disease (such as cirrhosis or hepatitis) and some types of leukemia. But the vitamin B12 test is not usually used to diagnose these problems.
• In rare cases, high levels may be found in people with diabetes or who are obese.

Low values

• Low levels of vitamin B12 may mean you have vitamin B12 deficiency anemia, which might be caused by problems with the absorption of the vitamin (such as pernicious anemia).
• Low levels may also occur following removal of part or all of the stomach (gastrectomy), gastric bypass surgery, or gastric stapling surgery, or following surgery to remove part of the small intestine where this vitamin is absorbed (terminal ileum).
• Low levels may mean an infection with a parasite called fish tapeworm is present.
• In rare cases, low levels may mean a person is not getting enough vitamin B12 in his or her food.
• Low levels are linked with hyperthyroidism or folic acid deficiency anemia.
• High levels of protein in the blood, such as from multiple myeloma, can falsely decrease blood vitamin B12 levels.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Taking certain medicines that might affect your test results. Tell your doctor all of the medicines that you take.
• Being pregnant or breast-feeding.
• Taking large doses of vitamin C.
• Drinking large amounts of alcohol.
• Having a test, such as a computed tomography (CT) scan, that used dyes in the past 7 days.
• Having pernicious anemia, which means you lack the substance (intrinsic factor) needed to absorb vitamin B12.

What To Think About

• Folic acid levels can be high in people who lack vitamin B12. A folic acid test is often done at the same time as a vitamin B12 test. For more information, see the topic Folic Acid.
• Methylmalonic acid is a substance in the blood that increases when vitamin B12 levels decrease. A methylmalonic acid (MMA) blood test may be done to help evaluate vitamin B12 test results.
• A change in homocysteine levels may also affect a change in vitamin B12 levels because of metabolism changes. For more information, see the topic Homocysteine.