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, (3) acute blood loss. Decreased production is covered in Chaps. 103, 105, and 107; increased destruction and acute blood loss are covered in this chapter.
All patients who are anemic as a result of either increased destruction or acute blood loss have two important elements in common: the anemia results from overconsumption of red cells from the peripheral blood, yet the supply of cells from the bone marrow (in the absence of coexisting marrow disease) is usually increased, as reflected by a reticulocytosis. On the other hand, 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.
With respect to primary etiology, anemias due to increased destruction of red cells, which we know as hemolytic anemias (HAs), may be inherited or acquired (Table 106–1). From the clinical point of view they may be more acute or more chronic, they may vary from mild to very severe, and 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. But before reviewing the individual types of HA it is appropriate to consider what they have in common.
Table 106–1 Classification of Hemolytic Anemias* |Favorite Table|Download (.pdf)
Table 106–1 Classification of Hemolytic Anemias*
|Intracorpuscular Defects||Extracorpuscular Factors|
|Familial (atypical) hemolytic uremic syndrome|
|Acquired||Paroxysmal nocturnal hemoglobinuria (PNH)|
Mechanical destruction (microangiopathic)
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 or with cold agglutinin disease may be diagnosed after years. This is due in large ...