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Vitamin B12 level

Cobalamin test; Pernicious anemia - vitamin B12 level

The vitamin B12 level is a blood test that measures how much vitamin B12 is in your blood.

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How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

You should not eat or drink for about 6 to 8 hours before the test.

Certain medicines may affect the results of this test. Your health care provider will tell you if you need to stop taking any medicines. Do not stop any medicine before talking to your provider.

Medicines that can affect the test result include:

• Colchicine
• H2 receptor blocking agents
• Metformin
• Neomycin
• Para-aminosalicylic acid
• Phenytoin
• Proton pump inhibitors

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

This test is most often done when other blood tests suggest a condition called megaloblastic anemia. Pernicious anemia causes a form of megaloblastic anemia caused by vitamin B12 deficiency due to poor vitamin B12 absorption. This can occur when the stomach makes less of the substance (called intrinsic factor) the body needs to efficiently absorb vitamin B12.

Your provider may also recommend a vitamin B12 test if you have certain nervous system symptoms. A low level of B12 can cause numbness or tingling in the arms and legs, weakness, and loss of balance.

Other conditions for which the test may be done include:

• Severe confusion (delirium)
• Loss of brain cognitive function (dementia)
• Nerve abnormalities, such as peripheral neuropathy

Normal Results

Normal values are 299 to 1054 picograms per milliliter (pg/mL), or 219 to 773 picomoles per liter (pmol/L).

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about what your specific test results mean.

What Abnormal Results Mean

Values of less than 299 pg/mL (219 pmol/L) are a possible sign of a vitamin B12 deficiency. People with this degree of deficiency are likely to have or develop symptoms.

Deficiency should be confirmed by checking the level of a substance in the blood called methylmalonic acid. A high level indicates a true B12 deficiency.

Causes of vitamin B12 deficiency include:

• Not enough vitamin B12 in diet (rare, except with a strict vegetarian diet)
• Diseases that cause malabsorption (for example, celiac disease and Crohn disease)
• Lack of intrinsic factor, a protein that helps the intestine absorb vitamin B12 efficiently
• Above normal body heat production (for example, with hyperthyroidism)
• Pregnancy

An increased vitamin B12 level is uncommon. Usually, excess vitamin B12 is removed in the urine.

Conditions that can increase B12 level include:

• Liver disease (such as cirrhosis or hepatitis)
• Myeloproliferative disorders (for example, polycythemia vera and chronic myelogenous leukemia)

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood buildup under the skin)
• Infection (a slight risk any time the skin is broken)

Related Information

References

Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 40.

Mason JB, Booth SL. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 199.

Stabler SP. Megaloblastic anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 150.

Review Date: 1/10/2026  

Reviewed By: Frank D. Brodkey, MD, FCCM, Associate Professor, Section of Pulmonary and Critical Care Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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