Doctors diagnose vitamin deficiency anemias through blood tests that check:
- The number and appearance of red blood cells. People with anemia have fewer red blood cells than normal. In vitamin deficiency anemias related to a lack of vitamin B-12 and folate, the red blood cells appear large and underdeveloped. In advanced deficiencies, the numbers of white blood cells and platelets also might be decreased and look abnormal under a microscope.
- The amount of folate, vitamin B-12 and vitamin C in your blood. Folate and vitamin B-12 levels are measured at the same time because these deficiencies can cause similar signs and symptoms.
Additional tests for B-12 deficiency
If blood tests reveal a vitamin deficiency, your doctor may perform other tests to determine the type and cause, such as:
- Antibodies test. Your doctor may draw a sample of your blood to check for antibodies to intrinsic factor. Their presence indicates pernicious anemia.
- Methylmalonic acid test. You may undergo a blood test to measure the presence of a substance called methylmalonic acid. The level of this substance is higher in people with vitamin B-12 deficiency.
- Schilling test. In this test, you first ingest a tiny amount of radioactive vitamin B-12. Then your blood is checked to see if your body absorbed the vitamin B-12. After that, you ingest a combination of radioactive vitamin B-12 and intrinsic factor. If the radioactive B-12 is absorbed only when taken with intrinsic factor, it confirms that you lack your own intrinsic factor.