Vitamin B12 Deficiency

Overview
Symptoms
Causes
Tests
Treatments
Sources

Tests
The anemia and large red blood cells of a vitamin B12 or folate deficiency are frequently detected during a routine CBC (Complete 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 ordered 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. May be ordered to monitor the effectiveness of treatment.

CBC (Complete Blood Count). A group of tests ordered routinely to screen for blood cell abnormalities. It measures cell types, quantities, and characteristics. With both B12 and folate deficiency anemia, the amount of hemoglobin 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 ordered to monitor the effectiveness of treatment.

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 no longer generally available.

Intrinsic Factor Binding Antibody. Interferes with B12 binding. It may be present in those with pernicious anemia. 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 anemia.

Parietal Cell Antibody. An antibody against the parietal cells that produce intrinsic factor. Present in a large percentage of pernicious anemia patients but may also be seen in other disorders.