Pernicious anemia is a decrease in red blood cells that occurs when the body cannot properly absorb vitamin B12 from the gastrointestinal tract. Vitamin B12 is necessary for the proper development of red blood cells.

Pernicious anemia is a type of megaloblastic anemia.

See also: Anemia

Macrocytic achylic anemia; Congenital pernicious anemia; Juvenile pernicious anemia; Vitamin B12 deficiency (malabsorption)

Pernicious anemia is caused by a lack of intrinsic factor. Intrinsic factor is a protein produced by the stomach that binds to vitamin B12. The combination of vitamin B12 and intrinsic factor is absorbed in the lower part of the small intestine. When the stomach does not make enough intrinsic factor, the intestine cannot properly absorb vitamin B12.

Very rarely, infants and children are born without the ability to produce enough intrinsic factor. Pernicious anemia that occurs at birth (congenital) is inherited. You need the defective gene from each parent to get it.

More common causes of pernicious anemia include:

• Weakened stomach lining (atrophic gastric mucosa)
• The body's immune system attacking the cells that make intrinsic factor (autoimmunity against gastric parietal cells)
• Autoimmunity against intrinsic factor itself

The disease begins slowly and may take decades to fully establish. Although the congenital form occurs in children, pernicious anemia usually does not appear before age 30 in adults. The average age at diagnosis is 60.

Risk factors include:

• Family history of the disease
• History of autoimmune endocrine disorders, including:

  • Addison's disease
  • Chronic thyroiditis
  • Graves disease
  • Hypoparathyroidism
  • Hypopituitarism
  • Myasthenia gravis
  • Secondary amenorrhea
  • Type 1 diabetes
  • Testicular dysfunction
  • Vitiligo
• Scandinavian or Northern European descent

In addition to pernicious anemia, other causes of vitamin B12 deficiency include:

• Certain drugs, including colchicine, neomycin, and para amino salicylic acid (used for tuberculosis treatment)
• Gastrointestinal disease (stomach removal surgery, celiac disease, Crohn's disease)
• Infection (intestinal parasites, too much growth of bacteria in the small intestine)
• Metabolic disorders (methylmalonic aciduria, homocystinuria)
• Nutritional problems (strict vegetarians who do not get vitamin B12 supplementation, poor diet in infancy, or poor nutrition during pregnancy)

Antony AC. Megaloblastic anemias. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 170.