How It Feels
The 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.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
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.
110–1500 picograms per milliliter (pg/mL)
81–1107 picomoles per liter (pmol/L) (SI units)
- 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 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.