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Pernicious anemia and the IF antibody

Raymond Lepage, PhD
Raymond Lepage, PhD
Senior Scientific Advisor

What is the purpose of this test?

This test is used to help diagnose pernicious anemia, the most common cause of vitamin B12 deficiency.

Vitamin B12 cannot be produced by the human body, therefore it must come from a person’s diet and/or supplements. Among its essential functions are the production of red blood cells and the proper functioning of the nervous system. To be absorbed into the blood, vitamin B12 must bind to the intrinsic factor, a protein produced by cells in the stomach called “parietal cells.” If the level of intrinsic factor is too low, either because the parietal cells are not functioning properly or the intrinsic factor is blocked, vitamin B12 cannot be absorbed into the blood, resulting in anemia and neuropathy along with abnormally large red blood cells.

What is an autoimmune disease?

The immune system is responsible for defending the body against attacks from foreign cells and organisms: bacteria, viruses, parasites and transplanted cells. Often, the immune system goes awry and confuses some of its own tissues as foreign. The production of antibodies against its own tissues is the cause of a large number of “autoimmune” diseases. Rheumatoid arthritis, lupus, pernicious anemia, juvenile diabetes and several thyroid disorders are autoimmune in origin. When the immune system produces antibodies against the intrinsic factor or the parietal cells in the stomach responsible for its production, it is called “pernicious anemia.”

When are these tests prescribed?

Intrinsic factor or parietal cell antibody assays are rarely prescribed. These assays usually follow a diagnosis of anemia (pallor, weakness, fatigue) or neuropathy (numbness or tingling in the hands or feet) that is accompanied by abnormally large red blood cells and abnormally low vitamin B12 levels.

What do the results mean?

The results of the intrinsic factor and parietal cell antibody assays are interpreted by taking into account other available information, particularly vitamin B12 levels and, at times, homocysteine and methylmalonic acid levels.

In the event of lowered vitamin B12 levels (with elevated methylmalonic or homocysteine acid levels), the presence of anti-intrinsic factor antibodies confirms a diagnosis of pernicious anemia in about half of all cases. In addition, anti-intrinsic factor antibodies may be “false positive” in some individuals with other autoimmune diseases of the thyroid or adrenal glands, even type 1 diabetes (juvenile diabetes). Therefore, a negative result does not completely eliminate a diagnosis of pernicious anemia, and in patients whose anti-intrinsic factor antibodies are negative, their doctor may refer to anti-parietal cell antibody levels, which should be positive in more than 90% of cases. It should be noted, however, that while anti-parietal cell antibodies are more sensitive for detecting pernicious anemia, they are less specific and may be positive under some conditions, including in 10% of the normal population.

Additional information:

An injection of vitamin B12 48 hours or less before the test may interfere with your result. Anemia associated with low levels of vitamin B12 usually takes several years to develop. Normal individuals have large reserves of vitamin B12, particularly in their liver.

For intrinsic factor antibodies

For parietal cell antibodies

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