Vitamin B12

Does this test have other names?

VB12, serum cobalamin

What is this test?

This test measures the level of vitamin 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 B12 from eating foods that come from animals, such as meat, eggs, and dairy products. Vitamin B12 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 doctor suspects that your vitamin B12 level is low. A low level of vitamin B12 is called vitamin B12 deficiency. You are more likely to have vitamin 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.

You may also need this test if you've been diagnosed with or your doctor suspects a disease called pernicious anemia. Pernicious anemia affects the lining of your stomach and makes it hard to absorb vitamin B12.

These are common symptoms of vitamin B12 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 doctor may order other tests to help find out the cause of your vitamin B12 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.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Vitamin B12 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 requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Certain conditions may affect your test results. These include:

  • Pregnancy

  • Recent blood transfusions

  • Smoking

Medications 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 doctor how long you need to fast before the test. You should not have a vitamin B12 injection before the test.