Vitamin B-12

VB12, serum cobalamin, antipernicious anemia factor

This test measures the level of vitamin B-12 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.

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 digestive surgery, or eat a vegan diet. People 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 pernicious anemia. Pernicious anemia involves a lack of a protein found in your stomach that 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

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 

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They 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 800 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 COPD (chronic obstructive pulmonary disease), heart failure, or a rare type of blood cancer called polycythemia vera.

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

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. 

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.

Follow your healthcare provider's directions about not eating or drinking for a specific time before the test. You may be able to drink water. 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 illegal drugs you may use.