hematology and oncology
Etiology of Anemia
Introduction
Anemia is a decrease in the number of red blood cells (RBCs), which leads to a decrease in hematocrit and hemoglobin content. (See also Red Blood Cell Production .) The RBC mass represents the balance between production and destruction or loss of RBCs. Thus, anemia can result from one or more of 3 basic mechanisms (see table Classification of Anemia by Cause ): Blood loss Overview of Decreased Erythropoiesis None Overview of Hemolytic Anemia (RBC destruction) Blood losscan be Acute Chronic Anemia does not develop until several hours after acute blood loss when interstitial fluid diffuses into the intravascular space and dilutes the remaining RBC mass. During the first few hours, however, levels of polymorphonuclear granulocytes, platelets, and, in severe hemorrhage, immature white blood cells and normoblasts may rise. Chronic blood loss results in anemia if loss is more rapid than can be replaced or, more commonly, if accelerated erythropoiesis depletes body iron stores (see Iron Deficiency Anemia ). Deficient erythropoiesishas myriad causes. Complete cessation of erythropoiesis results in a decline in RBCs of about 7 to 10%/week (1%/day). Impaired erythropoiesis, even if not sufficient to decrease the numbers of RBCs, often causes abnormal RBC size and shape. can be caused by intrinsic abnormalities of RBCs or by extrinsic factors, such as the presence of antibodies or complement on their surface, that lead to their early destruction. An Splenomegaly sequesters and destroys RBCs more rapidly than normal. Some causes of hemolysis deform as well as destroy RBCs. Hemolysis normally causes increased reticulocyte production unless iron or other essential nutrients are depleted or there is 