What Is the B12 Blood Test?

Vitamin B12, also known as cobalamin, is a nutrient that is vitally important to the creation of DNA and to the overall function of the nervous system. A lack of vitamin B12 in the body can lead to vitamin deficiency anemia. A simple blood test can be performed in your doctor’s office to test the levels of vitamin B12 in your blood. Once the test is performed, your doctor will discuss the results with you.


Your doctor may order a vitamin B12 test to be performed if you have symptoms indicating a deficiency. Elderly patients may exhibit signs of a deficiency that include sudden behavior changes, including depress, irritability and confusion. Other signs and symptoms include fatigue, general weakness, dizziness and a sore mouth. Tingling or burning in your hands and feet indicate neuropathy and could be caused by a lack of vitamin B12. If you’ve recently had a complete blood count performed, your doctor may order a B12 test if the results indicated an abnormality in your red blood cells, or an abnormally low hemoglobin count.

Testing Procedure

If your doctor orders the vitamin B12 test for you, you may have your blood drawn in your doctor’s office, hospital lab, or in a separate lab in your community. The test is fast and simple, taking only minutes to complete. For this test, a technician will place a tourniquet around your arm to help her locate your veins. Next, she will obtain a sample of blood from a vein using a small needle. You will feel a prick when the needle is inserted. The blood sample is sealed into a tube and then sent to the lab to be tested.


Depending on the speed of the lab and their current workload, your results may be available in a few hours to a day or two. Normally, a vitamin B12 value of less than 200 picograms per milliliter is considered a deficiency, although your doctor may have her own parameters for what requires treatment. For example, elderly patients may exhibit signs of deficiency when levels fall between 200 and 500 pg/mL.


If your doctor discovers a B12 deficiency, you may be prescribed B12 supplements through injection or by oral supplement. To determine the effectiveness of your treatment, the test will be repeated two to three months after the supplementation begins. Your doctor will discuss the treatment plan with you and answer any questions you may have.