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Pernicious Anemia
(Vitamin B-12 Deficiency)

Pernicious Anemia Overview

Pernicious anemia is a type of anemia (reduced number of red blood cells or hemoglobin in the body) due to the body's inability to absorb vitamin B-12 from the gastrointestinal tract. Symptoms from anemia are a result of the decreased capacity of the blood to carry oxygen and include fatigue and shortness of breath. In addition, the deficiency of vitamin B-12 also can damage the nervous system.

Vitamin B-12 is also known as cobalamin (Cbl). Animal products, both meat and dairy, are the only dietary sources of vitamin B-12 for humans. Because the body has stores of vitamin B-12, inadequate dietary intake must persist for years before a true deficiency of vitamin B-12 occurs. For this reason, the pernicious anemia usually takes years to establish and is most commonly diagnosed in adults with an average age of 60. Also, a rare, form of pernicious anemia is present at birth.

Pernicious anemia is a form of megaloblastic anemia. Megaloblastic anemia is characterized by an abnormally large type of red blood cell (megaloblast) that is formed by the bone marrow when vitamin B-12 or folic acid levels are low. Megaloblastic anemia can also develop with other conditions that affect the bone marrow and as an effect of some chemotherapy drugs.

Pernicious Anemia Causes

The decreased absorption of vitamin B-12 from the gastrointestinal tract in pernicious anemia is believed to result from an autoimmune process in which the body's immune system attacks the lining of the stomach. Antibodies are produced against intrinsic factor (IF), a protein made in the stomach that is necessary for the absorption of vitamin B-12. Normally, vitamin B-12 binds to intrinsic factor in the stomach, and this facilitates its absorption later when digestive products pass through the small intestine. The autoimmune process attacks the IF protein and lowers IF levels in stomach secretions. An autoimmune process directed at the stomach lining cells also occurs and results in a chronic form of stomach inflammation (gastritis) known as chronic atrophic gastritis.

Pernicious anemia is most common in Caucasian persons of northern European ancestry than in other racial groups. In this population, 10-20 cases per 100,000 persons are diagnosed each year. Pernicious anemia may occur in association with other autoimmune diseases such as autoimmune thyroid disease and vitiligo.

While pernicious anemia is defined as anemia resulting from inadequate absorption of vitamin B-12 from the gastrointestinal tract due to the autoimmune process described above, other causes of vitamin B-12 deficiency can also produce the characteristic signs and symptoms of pernicious anemia. Other potential causes of vitamin B-12 deficiency include surgical removal of the stomach or a portion of the stomach (gastrectomy), other gastrointestinal diseases such as celiac disease or Crohn's disease, infection, and poor nutrition.