Laboratory testing is used to detect a vitamin deficiency, determine its severity, establish it as the underlying cause of someone'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.
Ordered to diagnose or monitor B12 and folate deficiencies:
- B12 blood level. If low, a deficiency is indicated, but it does not identify the cause. A low level of intrinsic factor may be a cause, for example. This test also may be ordered to monitor the effectiveness of treatment.
- Folate level. Either serum or RBC folate levels may be tested; if either is low, it indicates a deficiency. The tests may also be ordered to monitor the effectiveness of treatment. Pregnant women may be given this test at prenatal checkups.
- CBC. This group of tests is ordered routinely to evaluate the health of blood cells. It determines the number of cell types and can give an indication of the physical characteristics of some of the cells. With both B12 and folate deficiencies, the amount of hemoglobin and the red blood cell 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.
- Methylmalonic acid (MMA). This test may be ordered to help detect mild or early B12 deficiency.
- Homocysteine. This test is seldom ordered but may be elevated in both B12 and folate deficiency.
Ordered to help determine the cause of a B12 deficiency:
- 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. This antibody can disrupt the production of intrinsic factor and is present in a large percentage of those with pernicious anemia, but it may also be seen in other autoimmune disorders.
- Gastrin. A hormone that regulates the production of acid in the stomach during the digestive process. Increased gastrin is sometimes seen in pernicious anemia.
- Schilling test. Once frequently ordered to confirm a diagnosis of pernicious anemia, this test is generally no longer available.