Pernicious Anemia

In this patient, the elevated serum gastrin level and the presence of anti­intrinsic factor antibodies pointed to pernicious anemia.

Gastrin is a hormone produced in the antrum that stimulates secretion of stomach acid. In patients with pernicious anemia, the antrum is usually spared, but the body of the stomach becomes atrophic. As acid production from the gastric body shuts down,

gastrin levels rise in a futile attempt to counter achlorhydria.

The term pernicious anemia, which was coined by a German physician in the 19th century, is

somewhat misleading. The modern definition is vitamin B12 deficiency caused by B12 malabsorption that results from a dearth of gastric intrinsic factor. The key to the disease is the lack of intrinsic factor-a gastrointestinal finding, not a hematologic one. As many as a third of patients in whom the gastric defect is diagnosed do not have megaloblastic anemia. In other words, nonanemic patients can have pernicious anemia.

It is thought to be an autoimmune disorder that results in antibody production against both intrinsic factor and the gastric parietal cells that make the factor. About 80% of patients with pernicious anemia have antibodies against parietal cells, and about 66% have antibodies against intrinsic factor. Parietal cell antibodies are not specific for pernicious anemia; they can occur in any patient with type A atrophic gastritis, a condition that is especially common in the elderly. Thus, parietal cell antibody testing is not appropriate for the diagnosis of pernicious anemia. Intrinsic factor antibody testing, on the other hand, is about 95% specific for pernicious anemia but has a low sensitivity.