(IFAB test)
Intrinsic factor is a protein that is produced by the parietal cells of the stomach. It binds to vitamin B12, thereby allowing its absorption by intestinal cells. In pernicious anemia, an autoimmune disorder, autoantibodies are formed against intrinsic factor leading to its deficiency. The lack of intrinsic factor then causes malabsorption of vitamin B12 and subsequent anemia. Autoantibodies can also be formed directly against the parietal cells which similarly leads to inadequate intrinsic factor activity and vitamin B12 deficiency.
A positive IFAB test result indicates the presence of circulating autoantibodies to intrinsic factor. The combination of megaloblastic anemia, low serum vitamin B12, and the presence of serum IFAB strongly supports the diagnosis of pernicious anemia.
