Historically, microscopy has been used to evaluate different forms of anemia, which has led to the development of a classification system based on erythrocyte morphology. This method has produced the categories of microcytic anemia, normocytic anemia and macrocytic anemia. The disorders that lead to macrocytic anemia comprise a heterogeneous group with a variety of known and postulated mechanisms.
Macrocytosis (mean corpuscular volume greater than 100 [mu][m.sup.3] [100 fL] is a fairly common finding. Between 1.7 percent and 3.6 percent of automated blood counts reveal macrocytosis. Of this group, up to 40 percent also show anemia. Table 1 lists the common causes of "macrocytosis.
Besides having megaloblastic anemia and low serum [B.sub.12] levels, patients with pernicious anemia may have antibodies to intrinsic factor (in about one-half of cases) and gastroparietal cells. There are two types of intrinsic factor antibody. On blocks vitamin [B.sub.12] binding to intrinsic factor, and the other binds to the intrinsic factor-[B.sub.12] complex, impairing absorption. In advanced cases, the patient may be pancytopenic. The Schilling test is used to document the low oral absorption of [B.sub.12] that is typical of pernicious anemia. Table 5 lists causes of [B.sub.12] deficiency.
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JOHN DAVENPORT, M.D., J.D. is a family physician at Kaiser Permanente Medical Center, Anaheim, Calif. He received his medical degree from the Medical University of South Carolina College of Medicine, Charleston, and his juris doctorate from Western State University of Law of Orange County, Fullerton, Calif. He attended undergraduate school at the Georgia Institute of Technology, Atlanta.
Adress correspondence to John Davenport, M.D., J.D., Kaiser Foundation Research Institute, Department of Medical Editing, 1800 Harrison St., 16th floor, Oakland, CA 94612-3429.
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