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DEFINITIONS

A finite life span is a distinct characteristic of red cells. Hence, a logical, time-honored classification of anemias is in three groups: (1) decreased production of red cells, (2) increased destruction of red cells, and (3) acute blood loss. Decreased production is covered in Chaps. 93, 94, and 98; acute blood loss in Chap. 97; increased destruction is covered in this chapter.

All patients who are anemic as a result of either increased destruction of red cells or acute blood loss have one important element in common: the anemia results from overconsumption of red cells from the peripheral blood, whereas the supply of cells from the bone marrow is normal (indeed, it is usually increased). On the other hand, these two groups differ in that the consequences of physical loss of red cells from the bloodstream or from the body itself, as in acute hemorrhage, is fundamentally different from destruction of red cells within the body, as in hemolytic anemias (HAs).

With respect to primary etiology, HAs may be inherited or acquired; from a 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 causes or to extracorpuscular causes (Table 96-1). But before reviewing the individual types of HA, it is appropriate to consider what general features they have in common, in terms of clinical aspects and of pathophysiology.

TABLE 96-1Classification of Hemolytic Anemiasa

GENERAL CLINICAL AND LABORATORY FEATURES

The clinical presentation of a patient with anemia is greatly influenced in the first place by whether the onset is abrupt or gradual, and HAs are no exception. A patient with autoimmune HA or with favism may be a medical emergency, whereas a patient with mild hereditary spherocytosis (HS) or with cold agglutinin disease (CAD) ...

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