The immune system defends us against attacks from foreign cells and organisms, such as bacteria and viruses. But it often goes haywire and sees some of its own tissues as foreign. The production of antibodies against the body’s own tissues is responsible for many autoimmune diseases such as rheumatoid arthritis, lupus and juvenile diabetes. When the immune system produces antibodies against the cells of the stomach lining (parietal cells), there is a drop in the secretion of intrinsic factor, a protein essential for intestinal absorption of vitamin B12. In turn, vitamin B12 deficiency leads to a decrease in the production of red blood cells by the bone marrow, which causes “pernicious” anemia.
A negative result does not completely rule out the possibility of pernicious anemia: at least 10% of individuals with pernicious anemia test negative for anti-parietal antibodies. A positive result can also be found in 50% of individuals with gastritis (inflammation of the stomach lining), 30% of people with thyroiditis (inflammation of the thyroid gland) and a wide variety of other autoimmune disorders. Testing for intrinsic factor antibodies is more useful in these situations.