Diagnosis and classification of pernicious anemia.

Pernicious anemia (PA) is a complex disorder consisting of hematological, gastric and immunological alterations. Diagnosis of PA relies on histologically proven atrophic body gastritis, peripheral blood examination showing megaloblastic anemia with hypersegmented neutrophils, cobalamin deficiency and antibodies to intrinsic factor and to gastric parietal cells. Anti-parietal cell antibodies are found in 90% of patients with PA, but have low specificity and are seen in atrophic gastritis without megaloblastic anemia as well as in various autoimmune disorders. Anti-intrinsic factor antibodies are less sensitive, being found in only 60% of patients with PA, but are considered highly specific for PA. The incidence of PA increases with age and is rare in persons younger than 30 years of age. The highest prevalence is seen in Northern Europeans, especially those in the United Kingdom and Scandinavia, although PA has been reported in virtually every ethnic group. Because of the complexity of the diagnosis, PA prevalence is probably underestimated and no reliable data are available on the risk of gastric cancer as the end-stage evolution of atrophic gastritis in these patients.