vitamin B12 test measures the amount of vitamin B12 in the blood. The body needs this
B vitamin to make blood cells and to maintain a healthy nervous system.
Vitamin B12 is found in
animal products such as meat, shellfish, milk, cheese, and eggs. Most people who eat
animal products are not likely to develop vitamin B12 deficiency anemia unless their bodies
can't absorb it from food. Strict vegetarians (vegans) who do not eat animal products
and babies of mothers who are strict vegetarians are at increased risk for developing
anemia and should take a supplement containing vitamin B12. Vitamin B12 is stored
in the liver for a year or more, which reduces a person's risk of anemia.
B12 is usually measured at the same time as a folic acid test, because a lack of either one
or both can lead to a form of anemia called megaloblastic anemia. Lack of vitamin B12 also
affects the nervous system.
Why It Is Done
A vitamin B12 test
is used to:
Check for vitamin B12 deficiency anemia. There are several
risk factors for this anemia, such as those who have had stomach or intestinal surgery,
small intestine problems, or people with a family history of this anemia.
the cause of certain types of anemia, such as megaloblastic anemia.
See if vitamin B12 deficiency anemia is present
after a person has been diagnosed with atrophic gastritis.
How To Prepare
not eat or drink (other than water) for 10 to 12 hours before the test.
It Is Done
Your health professional drawing blood will:
elastic band around your upper arm to stop the flow of blood. This makes the veins
below the band larger so it is easier to put a needle into the vein.
the needle site with alcohol.
Put the needle into the vein. More than one
needle stick may be needed.
Attach a tube to the needle to fill it with blood.
the band from your arm when enough blood is collected.
Put a gauze pad or
cotton ball over the needle site as the needle is removed.
Put pressure on
the site and then put on a bandage.
How It Feels
blood sample is taken from a vein in your arm. An elastic band is wrapped around your
upper arm. It may feel tight. You may feel nothing at all from the needle, or you
may feel a quick sting or pinch.
There is very little chance
of a problem from having a blood sample taken from a vein.
You may get
a small bruise at the site. You can lower the chance of bruising by keeping pressure
on the site for several minutes.
In rare cases, the vein may become swollen
after the blood sample is taken. This problem is called phlebitis. A warm compress
can be used several times a day to treat this.
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.
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.
rare cases, low levels may mean a person is not getting enough vitamin B12 in his
or her food.
Fischbach FT, Dunning
MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia:
Lippincott Williams and Wilkins.
This information does not replace the advice of a doctor.
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