Vitamin B12 and Folate Deficiency

Tests
The anaemia and large red blood cells of a vitamin B12 or folate deficiency are frequently detected during a routine FBC (Full Blood Count) test. Laboratory testing is used to detect a deficiency, determine its severity, establish the underlying cause of the deficiency, and to monitor the effectiveness of treatment.

Laboratory Tests
Frequently requested to diagnose and monitor B12 and folate deficiency:

• B12. If low, a deficiency is indicated, but it does not identify the cause. If normal, a folate deficiency may still be present.
• FBC (Full Blood Count). A group of tests requested routinely to screen for blood cell abnormalities. It measures cell types, quantities, and characteristics. With both B12 and folate deficiency anaemia, the amount of haemoglobin may be low and the red blood cells (RBCs) are abnormally large (macrocytic or megaloblastic). White blood cells and platelets also may be decreased.
• Folate. Either serum or RBC folate may be tested. Some believe that the RBC folate is more clinically relevant. If either is low, it indicates a deficiency. If normal, a B12 deficiency may still be present. May be used to monitor the effectiveness of treatment. High serum folate may be a sign of bacterial overgrowth in the bowels.

Seldom but sometimes used to diagnose B12 and folate deficiency:

• Methylmalonic Acid (MMA). A blood or urine test, sometimes used to help detect mild or early B12 deficiency, or to exclude true B12 deficiency in cases of a misleadingly low laboratory B12 result.
• Homocysteine. Occasionally requested. May be elevated in both B12 and folate deficiency.

Requested to help determine the cause of a B12 deficiency:

• Schilling Test. Once frequently used to confirm a diagnosis of pernicious anaemia. This test is used less frequently nowadays.
• Intrinsic factor Binding Antibody. Interferes with B12 binding. It may be present in those with pernicious anaemia. This is a specialized test that is not commonly available.
• Intrinsic Factor Blocking Antibody. A protein that prevents B12 from binding to intrinsic factor. It is present in more than 50 percent of all patients with pernicious anaemia.
• Parietal Cell Antibody. An antibody against the parietal cells that produce intrinsic factor. Present in nearly all cases of pernicious anaemia but may also be seen in other disorders.