Your doctor will ask you about your diet and about any family history of anemia. Your doctor also will review your medical history for medical illnesses (diabetes, immune disorders) or surgeries, such as stomach removal, that can lead to B12 deficiency.
Your doctor may suspect that you have vitamin B12 deficiency based on your medical history and symptoms. To confirm the diagnosis, he or she will examine you and order laboratory tests. During the physical examination, your doctor will look for a red, beefy tongue, pale or yellowish skin, a rapid pulse and heart murmurs resulting from an anemia-related increase in blood flow demands on the heart. Laboratory tests will include:
Standard blood tests to measure the level of red blood cells and check their appearance - In vitamin B12 deficiency, red blood cells are unusually large and appear abnormal.
Blood tests to measure B12 levels - Levels of iron and folate also may be measured to check for deficiencies in these nutrients.
Blood test to measure methylmalonic acid level - The blood level of methylmalonic acid increases when a person has B12 deficiency.
Blood tests for intrinsic factor antibody - Your doctor may order special tests for antibody levels to determine if you have pernicious anemia. Most people who lack intrinsic factor in their stomach have these antibodies in their blood.
Bone marrow biopsy - Occasionally, a bone marrow biopsy is done to help confirm the diagnosis. In this procedure, a small sample of bone marrow is taken by inserting a needle into the pelvic bone just below the waist on either side of the spine. The bone marrow sample is examined in a laboratory to look for other causes of anemia and red blood cell abnormalities.
With proper treatment, symptoms of vitamin B12 deficiency begin to improve within a few days. In vegans and other people whose B12 deficiency is diet-related, oral B12 supplements and a diet designed to increase consumption of vitamin B12 should cure the condition. People with pernicious anemia or people who cannot absorb vitamin B12 from their intestines will need injections of vitamin B12 every one to three months indefinitely.