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How Do They Test for B12?

Vitamin B12 deficiency is diagnosed using a blood test that measures the amount of vitamin B12 found in the blood. This test is typically done in conjunction with a test for folate levels. A deficiency of vitamin B12 can lead to anemia, so the test is often done when symptoms of anemia appear or when a complete blood count test reveals low hemoglobin levels.

  1. Vitamin B12 Deficiency

    • Aside from suspecting vitamin B12 deficiency based on a complete blood count test, there are several symptoms that may indicate a deficiency. The physiological indications of a vitamin B12 deficiency include confusion, fatigue and paranoia. There are also digestive symptoms, including malabsorption, diarrhea and loss of appetite, and possible tingling or numbness in the extremities.

    Why the Test Is Performed

    • The vitamin B12 test is done to check for vitamin B12 deficiency anemia or to help identify the cause of anemia discovered in a complete blood count test. Vitamin B12 deficiency can also cause peripheral neuropathy and dementia, so the test can be used to help find the cause of these conditions. Finally, the test is done in patients where malabsorption in the digestive tract is known or suspected, as digestive issues can lead to vitamin B12 deficiency.

    What to Expect

    • The blood test for Vitamin B12 requires drawing blood from a vein. The most common location for blood draw is on the inside of the elbow. The patient should not to eat for several hours before the test is done.

    Complications

    • There are few complications with the vitamin B12 test. It is a blood test, so all possible complications come from drawing the blood, a very low-risk procedure. It is possible that the site of the blood draw may bruise or swell. If you suffer from a bleeding disorder or are taking a blood thinner, it is also possible that the site may continue to bleed.

    Other Information

    • The vitamin B12 test measures the amount of vitamin B12 in the blood serum. Some drugs can decrease the level of vitamin B12, including oral contraceptives, some antibiotics and alcohol. A high level of vitamin B12 is sometimes observed in patients with leukemia or liver problems, but vitamin B12 levels are not usually monitored in these instances.

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