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Vitamin B12 and Folate

Does this test have other names?

Cobalamin, Cbl, folic acid, FA

What is this test?

This test measures the levels of vitamin B12 and folate in your blood.

Your body needs vitamin B12, also called cobalamin, and folate, also called folic acid, to function normally. Both nutrients play important roles in creating red blood cells and making DNA and RNA to help build cells. B12 also helps your nervous system function as it should.

B12 is found in fortified cereals and animal products like fish, meat, eggs, and dairy. It's also in dietary supplements, as cyanocobalamin.  Folate is found naturally in green leafy vegetables, fruits, and beans, and it's added to enriched cereals and grains.

People who have pernicious anemia may have low B12 levels because this condition prevents them from absorbing B12. A low folate level can also be the result of a poor diet or alcohol abuse.

Why do I need this test?

You may have this test if you are taking medications that could interfere with how your body absorbs B12 or folate. You may also have this test if you have a disease or condition that could lead to B12 deficiency. Symptoms of B12 deficiency include:

  • Fatigue

  • Headaches

  • Numbness or "pins and needles" in the hands and feet

  • Difficulty walking

  • Memory loss

  • Difficulty thinking normally

  • Changes in mood

Symptoms of having too little folate are diarrhea, weight loss, and other vague symptoms that could be caused by many other conditions.

It's important that women who are pregnant, thinking of becoming pregnant, or breastfeeding have enough folate.

This test measures both vitamin B12 and folate, but either of these nutrients can be measured separately in different lab tests. Your doctor may order this combined test if you have a condition for which it's important to know both levels.

What other tests might I have along with this test?

Your doctor may also order these tests:

  • Homocysteine and methylmalonate, or methylmalonic acid. These substances can build up in your body if you have a B12 or folate deficiency.

  • Red blood cell

  • Pernicious anemia. This includes measuring levels of gastrin, pepsinogen I, pepsinogen II, and antibodies against a substance called intrinsic factor.

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.

Results are given in nanograms per milliliter (ng/mL). A normal range for vitamin B12 is 190 to 900 ng/mL.

If your B12 results are low, it may mean you have:

  • Pernicious anemia

  • Stomach issues, such as lack of stomach acid, that make it difficult to absorb the vitamin

  • Folate deficiency

Your diet can also lead to B12 deficiency. Some vegetarians or vegans who don't eat eggs or other dairy products may develop this deficiency.

Your B12 results may also be higher or lower if you have had recent nuclear medicine studies using radiation. They can mean that you have:

  • Severe liver disease

  • Chronic granulocytic leukemia

If the test is done on your blood plasma, a normal range for folate is 2 to 10 ng/mL. If the test is done on red blood cells, a normal range is 140 to 960 ng/mL.

If your folate results are low, it may mean you have:

  • A diet that doesn't provide enough folate

  • Difficulty absorbing the nutrient

  • Alcohol abuse

  • B12 deficiency

  • Hemolytic anemia

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?

Being pregnant can affect your results, as can eating foods that are high or low in folate. Alcohol use can also affect your results. Certain medications can also affect your results. These include:

  • Birth control pills

  • Methotrexate

  • Trimethoprim

  • Phenytoin

  • Azulfidine

How do I get ready for this test?

Tell your health care provider about medical conditions you have, and how much alcohol you drink regularly. In addition, be sure your doctor 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.