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Vitamin B12 Test



  • The vitamin B12 test is a blood test to check the amount of this vitamin in your child’s blood. It can help diagnose medical problems such as anemia.
  • A small amount of blood is taken from a heel stick or from a vein in your child’s arm with a needle and sent to a lab.
  • Talk to your healthcare provider about what the test results mean and ask any questions you have.


What is the vitamin B12 test?

This test measures the amount of vitamin B12 in your child’s blood. The body needs vitamin B12 to make blood cells. Nerve cells and the brain need vitamin B12 to work normally as well. Your child can get vitamin B12 from food and supplements.

Why is it done?

This test is done to see if your child’s body is absorbing enough vitamin B12. If your child has anemia, it may be done to see if the anemia is caused by a lack of vitamin B12.

How do I prepare my child for this test?

  • The vitamin B12 test is often done with a test for the level of folic acid in your child’s blood. If your folic acid level is being tested, your healthcare provider will tell you when your child should stop eating and drinking before the test. Food and drink before the test may affect the results.
  • Your child may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your child’s healthcare provider knows about any medicines, herbs, or supplements that your child is taking. Ask your provider before stopping any of your child’s regular medicines.
  • Talk to your healthcare provider if you have any questions about the test.

How is the test done?

Your child's healthcare provider makes a tiny cut in a baby's heel to get a small amount of blood to test.

A small amount of blood is taken from a finger with a fingerstick or from a vein in your child’s arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the result of your child’s test.

What does the test result mean?

Some of the reasons your child’s vitamin B12 level may be lower than normal are:

  • Your child does not get enough vitamin B12 from the food he eats. This is unusual unless your child is a vegan and eats no animal products, or if you are a vegan and are breastfeeding.
  • Your child doesn’t have enough acid in his stomach. Stomach acid is needed to get vitamin B12 out of the food your child eats.
  • Your child has pernicious anemia, which is an immune system disorder that makes it hard for the intestines to absorb B12.
  • Your child has had an intestinal illness or intestinal surgery, which makes it hard for the intestines to absorb vitamin B12.

A low blood level of vitamin B12 is called vitamin B12 deficiency.

Some of the reasons your child’s vitamin B12 level may be higher than normal are:

  • Your child has too much vitamin B12 in his diet.
  • Your child has liver disease, such as cirrhosis or hepatitis.
  • Your child has certain other conditions, such as some types of leukemia.

What if my child’s test result is not normal?

Test results are only one part of a larger picture that takes into account your child’s medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about the result and ask questions, such as:

  • If your child needs more tests
  • What kind of treatment your child might need
  • What lifestyle, diet, or other changes your child might need to make
Developed by RelayHealth.
Pediatric Advisor 2015.3 published by RelayHealth.
Last modified: 2015-03-25
Last reviewed: 2015-03-24
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright ©1986-2015 McKesson Corporation and/or one of its subsidiaries. All rights reserved.
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