Vitamin B12 level
Definition
The vitamin B12 level is a blood test that measures how much
Alternative Names
Cobalamin test; Pernicious anemia - vitamin B12 level
How the Test is Performed
A
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
- Neomycin
- Para-aminosalicylic acid
- Phenytoin
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.
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:
- Sudden severe confusion (
delirium ) - Loss of brain function (
dementia ) Dementia due to metabolic causes - Nerve abnormalities, such as
peripheral neuropathy
Normal Results
Normal values are 160 to 950 picograms per milliliter (pg/mL), or 118 to 701 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 160 pg/mL (118 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 andCrohn disease ) - Lack of
intrinsic factor , a protein that helps the intestine absorb vitamin B12 - 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 orhepatitis ) -
Myeloproliferative disorders (for example,
polycythemia vera andchronic 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)
References
Marcogliese AN, Hensch L. Resources for the hematologist: interpretive comments and selected reference values for neonatal, pediatric, and adult populations. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 159.
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: 03/31/2024
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