Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss (Part 1) Harrison's Internal Medicine > Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss Definitions A finite life span is a distinct characteristic of red cells. Hence, a logical, time-honored classification of anemias comprises three groups: decreased production of red cells, increased destruction of red cells, and acute blood loss. Red cell destruction and acute loss, both associated with increased reticulocyte production, are covered in this chapter. Red cell production defects are discussed in Chaps. 98, 99, and 100. Physical loss of red cells from the bloodstream—which in most cases also means physical loss from the body—is fundamentally different from destruction of red cells within the body. Therefore the clinical aspects and the pathophysiology of anemia in these two groups of patients are quite different, and they will be considered separately. Hemolytic Anemias Anemias due to increased destruction of red cells, or hemolytic anemias (HAs), may be inherited or acquired. From the clinical point of view, they may be more acute or more chronic, and they may vary from mild to very severe. The site of hemolysis may be predominantly intravascular or extravascular. With respect to mechanisms, HAs may be due to intracorpuscular or extracorpuscular causes (Table 101-1); however, before reviewing the individual types of HAs, it is appropriate to consider what they have in common. Table 101-1 Classification of Hemolytic Anemias a Intracorpuscular Defects Extracorpuscular Factors Hereditary Hemoglobinopathies Familial hemolytic uremic syndrome (HUS) Enzymopathies Membrane-cytoskeletal defects Acquired Paroxysmal nocturnal hemoglobinuria (PNH) Mechanical destruction (microangiopathic) Toxic agents Drugs Infectious Autoimmune a There is a strong correlation between hereditary causes and intracorpuscular defects, because such defects are due to inherited mutations; the one exception is PNH, becaus e the defect is due to an acquired somatic mutation. There is also a strong correlation between acquired causes and extracorpuscular factors; the one exception is familial HUS, because here an inherited abnormality allows excessive complement activation, w ith bouts of production of membrane attack complex capable of severely damaging normal cells. General Clinical and Laboratory Features The clinical presentation of a patient with anemia is greatly influenced by whether the onset is abrupt or gradual, and HA is no exception. A patient with autoimmune hemolytic anemia or with favism may be a medical emergency, whereas a patient with mild hereditary spherocytosis or with cold agglutinin disease may be diagnosed after years. This is due in large measure to the remarkable ability of the body to adapt to anemia when it is slowly progressing (Chap. 58). What differentiates HA from other anemias is that the patient has signs and symptoms arising directly from hemolysis (Table 101-2). At the clinical level, the main sign is jaundice; in addition, the patient may report discoloration of the urine. In many cases of HA, the spleen is enlarged because it is a preferential site of hemolysis; in some cases the liver may be enlarged as well. In all severe congenital forms of HA, skeletal changes may be noted due to over-activity of the bone marrow (although they are never as severe as in thalassemia). . Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss (Part 1) Harrison's Internal Medicine > Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss. clinical aspects and the pathophysiology of anemia in these two groups of patients are quite different, and they will be considered separately. Hemolytic Anemias Anemias due to increased destruction. classification of anemias comprises three groups: decreased production of red cells, increased destruction of red cells, and acute blood loss. Red cell destruction and acute loss, both associated