Laboratory testing is used to detect a vitamin deficiency, determine its severity, establish it as the underlying cause of the patient's symptoms, and to monitor the effectiveness of treatment. The anemia and large red blood cells (RBCs) associated with a vitamin B12 or folate deficiency are often initially detected during a routine complete blood count (CBC). Additional laboratory testing is performed as follow up to identify the specific deficiency.
Frequently ordered to diagnose or monitor B12 and folate deficiencies:
- B12. If low, a deficiency is indicated, but it does not identify the cause; may be ordered to monitor the effectiveness of treatment.
- Folate. Either serum or RBC folate levels may be tested; if either is low, it indicates a deficiency; may be ordered to monitor the effectiveness of treatment.
- Complete blood count (CBC). A group of tests ordered routinely to screen for blood cell abnormalities. It measures cell types, quantities, and characteristics. With both B12 and folate deficiencies, the amount of hemoglobin and RBC count may be low, and the RBCs are abnormally large (macrocytic or megaloblastic), resulting in an anemia. White blood cells and platelets also may be decreased.
Seldom but sometimes used to diagnose B12 and folate deficiency:
- Methylmalonic acid (MMA). Sometimes ordered to help detect mild or early B12 deficiency.
- Homocysteine. Occasionally ordered; may be elevated in both B12 and folate deficiency.
Ordered to help determine the cause of a B12 deficiency:
- Schilling test. Once frequently ordered to confirm a diagnosis of pernicious anemia, this test is generally no longer available.
- Intrinsic factor antibody. The antibody prevents intrinsic factor from carrying out its function, that is, to carry vitamin B12 and allow B12 to be absorbed at a specific segment of the small intestine.
- Parietal cell antibody. An antibody against the parietal cells that produce intrinsic factor; present in a large percentage of those with pernicious anemia but may also be seen in other autoimmune disorders.