The vitamin B12 level is a blood test that measures how much vitamin B12 is in your blood.
A blood sample is needed.
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:
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.
This test is most often done when other blood tests suggest a condition called megaloblastic anemia. Pernicious anemia is a form of megaloblastic anemia caused by poor vitamin B12 absorption. This can occur when the stomach makes less of the substance the body needs to properly 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:
Normal values are 160 to 950 picograms per milliliter (pg/mL), or 118 to 701 picomole 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.
Values of less than 160 pg/mL (118 pmol/L) are a possible sign of a vitamin B12 deficiency. People with this deficiency are likely to have or develop symptoms.
Older adults with a vitamin B12 level less than 100 pg/mL (74 pmol/L) may also have 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:
An increased vitamin B12 level is uncommon. Usually, excess vitamin B12 is removed in the urine.
Conditions that can increase B12 level include:
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:
Reviewed By: Richard LoCicero, MD, private practice specializing in hematology and medical oncology, Longsteet Cancer Center, Gainesville, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.