Anti-intrinsic factor antibodies

Pernicious anemia arises when vitamin B,2 deficiency blocks the metabohsm of folic acid, leading to functional folate deficiency. This impairs erythropoiesis, causing immature precursors of erythrocytes to be released into the circulation (megaloblastic anemia). The commonest cause of pernicious anemia is failure of the absorption of vitamin B,2 rather than dietary deficiency. This can be due to failure of intrinsic factor secretion caused by autoimmune disease of parietal cells or to generation of anti-intrinsic factor antibodies. 

Other potentially useful tests include antibody testing and serum gastrin levels. Positive anti-intrinsic factor antibodies may be present in approximately half of patients with pernicious anemia, but is highly specific for the disease. Additionally, an estimated 85% of patients have anti-parietal cell antibodies, but they are nonspecific, as 3% to 10% of healthy patients have these antibodies. Fasting serum gastrin levels are elevated in more than 70% of patients with cobalamin deficiency and may be useful in assessing patients with borderline... 

About 70% of patients also have anti-intrinsic factor antibodies in plasma, saliva and gastric juice. Although the oral administration of partially purified preparations of intrinsic factor will restore the absorption of vitamin B in many patients with pernicious anaemia, this can result eventually in the production of anti-intrinsic factor antibodies, so parenteral administration of vitamin B is the preferred means of treatment. For patients who secrete anti-intrinsic factor antibodies in the saliva or gastric juice, oral intrinsic factor will be useless. 

The test can be repeated, giving intrinsic factor orally together with the radioactive vitamin B if the impaired absorption was due to a simple lack of intrinsic factor, and not to anti-intrinsic factor antibodies in saliva or gastric juice, then a normal amount of the radioactive material should be absorbed and excreted. 

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