Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss (Part 1)

Harrisons Internal Medicine Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood LossDefinitions 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...
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Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss (Part 1) Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss (Part 1) Harrisons Internal Medicine > Chapter 101. Hemolytic Anemias andAnemia 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: decreasedproduction of red cells, increased destruction of red cells, and acute blood loss.Red cell destruction and acute loss, both associated with increased reticulocyteproduction, are covered in this chapter. Red cell production defects are discussedin Chaps. 98, 99, and 100. Physical loss of red cells from the bloodstream—which in most cases alsomeans physical loss from the body—is fundamentally different from destruction ofred cells within the body. Therefore the clinical aspects and the pathophysiologyof anemia in these two groups of patients are quite different, and they will beconsidered 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 bemore acute or more chronic, and they may vary from mild to very severe. The siteof hemolysis may be predominantly intravascular or extravascular. With respectto mechanisms, HAs may be due to intracorpuscular or extracorpuscular causes(Table 101-1); however, before reviewing the individual types of HAs, it isappropriate to consider what they have in common. Table 101-1 Classification of Hemolytic Anemiasa Intracorpuscular Extracorpuscular Defects Factors Hereditary Hemoglobinopathies Familial hemolytic uremic syndrome (HUS) Enzymopathies Membrane-cytoskeletal defects Acquired Paroxysmal nocturnal Mechanical destruction hemoglobinuria (PNH) (microangiopathic) Toxic agents Drugs Infectious Autoimmune a There is a strong correlation between hereditary causes andintracorpuscular defects, because such defects are due to inherited mutations; theone exception is PNH, because the defect is due to an acquired somatic mutation.There is also a strong correlation between acquired causes and extracorpuscularfactors; the one exception is familial HUS, because here an inherited abnormalityallows excessive complement activation, with bouts of production of membraneattack complex capable of severely damaging normal cells. General Clinical and Laboratory Features The clinical presentation of a patient with anemia is greatly influenced bywhether the onset is abrupt or gradual, and HA is no exception. A patient withautoimmune hemolytic anemia or with favism may be a medical emergency,whereas a patient with mild hereditary spherocytosis or with cold agglutinindisease may be diagnosed after years. This is due in large measure to theremarkable 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 andsymptoms arising directly from hemolysis (Table 101-2). At the clinical level, themain sign is jaundice; in addition, the patient may report discoloration of theurine. In many cases of HA, the spleen is enlarged because it is a preferential siteof hemolysis; in some cases the liver may be enlarged as well. In all severecongenital forms of HA, skeletal changes may be noted due to over-activity of thebone marrow (although they are never as severe as in thalassemia).