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Vitamin B12: About This Test

What is it?

This blood test measures the amount of vitamin B12 in your blood. Your body needs this B vitamin to make blood cells and to keep your nervous system healthy.

Why is this test done?

This test is used to:

  • Check for vitamin B12 deficiency anemia. It's often done for those who've had stomach or bowel surgery. It's also important for those who have problems of the small intestine or a family history of this anemia.
  • Check on the B12 level for someone who is on a diet that restricts certain foods (such as vegan).
  • Find the cause of other types of anemia.
  • Help find the cause of a decrease in mental abilities.
  • Find the cause of other symptoms. This can include tingling or numbness of the arms or legs.

How can you prepare for the test?

  • In general, you don't need to prepare before having this test. But it’s important to let your doctor know if you take any medicines, including vitamins and natural health products. Some medicines may affect the test results. Your doctor will let you know if you need to stop taking any medicines before you have the test.

What happens during the test?

  • A health professional takes a sample of your blood.

What else should you know about the test?

  • Your results will include an explanation of what a "normal" result is. This is called a "reference range." It is just a guide. 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 may still be normal for you.
  • Vitamin B12 is usually measured at the same time as folic acid is tested, because a lack of either one can lead to a form of anemia called megaloblastic anemia.

How long does the test take?

The test will take a few minutes.

What happens after the test?

  • You will probably be able to go home right away.
  • You can go back to your usual activities right away.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

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