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Vitamin B-12

Does this test have other names?

VB12, serum cobalamin

What is this test?

This test measures the level of vitamin B-12 (or B12) in your blood. You need this vitamin to make red blood cells and for your nervous system to function as it should.

You get vitamin B-12 from eating foods that come from animals, such as meat, eggs, and dairy products. Vitamin B-12 is also added to some cereals. You can also take this vitamin as a supplement in pill form.

Why do I need this test?

You may need this test if your healthcare provider suspects that your vitamin B-12 level is low. A low level of vitamin B-12 is called vitamin B-12 deficiency. You are more likely to have vitamin B-12 deficiency if you are an older adult, have a digestive disorder called malabsorption, have had gastrointestinal surgery, or eat a vegan diet. Women who are pregnant or breastfeeding and eat a vegetarian-type diet are at high risk for this deficiency in themselves and their babies.

You may also need this test if you've been diagnosed with or your healthcare provider suspects a disease called pernicious anemia. Pernicious anemia affects the lining of your stomach and makes it hard to absorb vitamin B-12.

These are common symptoms of vitamin B-12 deficiency:

  • Fatigue

  • Weakness

  • Weight loss

  • Tingling or numbness of the hands and feet

  • Constipation

  • Poor balance

  • Confusion

  • Depression

  • Memory loss

  • Soreness of the mouth or tongue

What other tests might I have along with this test?

Your healthcare provider may order other tests to help find out the cause of your vitamin B-12 deficiency. These tests may include:

  • Complete blood count

  • Peripheral blood smear, which involves looking at your blood cells under a microscope

  • Folic acid level. This vitamin is also important for red blood cell production.

  • Methylmalonic and homocysteine levels, which are part of vitamin B-12 and folate metabolism 

What do my test results mean?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

Vitamin B-12 is measured in picograms per milliliter (pg/mL). Normal results are:

  • 200 to 835 pg/mL for adults

  • 160 to 1,300 pg/mL for newborns

If your results are low, you may have:

  • Pernicious anemia

  • Malabsorption from inflammatory bowel disease or other causes

  • Poor absorption because of surgery

  • Tapeworm infection

  • Too little intake of animal protein

  • Folic acid deficiency

  • Iron deficiency

If your levels are high, you may have:

  • Liver or kidney disease

  • Diabetes

  • Obesity

  • White blood cell cancer

High levels may also mean that you have chronic obstructive pulmonary disease, congestive heart failure, or a thickening of the blood called polycythemia vera.

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

What might affect my test results?

Certain conditions may affect your test results. These include:

  • Pregnancy

  • Recent blood transfusions

  • Smoking

Medicines in general may also affect your results. Specific medicines include supplements of vitamin A or C and birth control pills.

How do I get ready for this test?

You must fast before this test. You may be able to drink water, but you should not eat or drink anything else after midnight on the night before the test. If you are not having the test in the morning, ask your healthcare provider how long you need to fast before the test. You should not have a vitamin B-12 injection before the test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.

Online Medical Reviewer: Freeborn, Donna, PhD, CNM, FNP
Online Medical Reviewer: Haldeman-Englert, Chad, MD
Date Last Reviewed: 12/1/2017
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