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Anemia is a common problem, affecting an estimated one third of the world’s population. By itself, anemia is not so much a disease as a symptom of an underlying process. Worldwide, the most common causes of anemia include iron deficiency, thalassemia, hemoglobinopathies, and folate deficiencies. Within the U.S., the most common causes are iron deficiency, thalassemia, and anemia of chronic disease. Not only is anemia common in the general population, the prevalence of anemia increases with age. Given the ubiquity of this entity, patients with anemia will present to the ED, some of whom will be symptomatic from their anemia, while in others, this will be an unexpected finding.

Anemia is defined as a reduced concentration of red blood cells (RBCs) from an individual’s baseline level.1–5 In healthy persons, normal erythropoiesis ensures that the number of RBCs present is adequate to meet the body’s demand for oxygen and that erythrocyte destruction equals production. The average life span of the circulating erythrocyte is approximately 120 days. Any process or condition that impairs production, increases the rate of destruction, or increases the loss of erythrocytes will result in anemia if the body cannot produce enough new cells to keep up with the loss. In patients with anemia, more than one mechanism may be operant.

Quantification of the erythrocyte concentration is reflected in the RBC count per microliter, hemoglobin concentration, or hematocrit (percentage of RBC mass to blood volume). Normal RBC values for adults vary slightly between males and females (Table 226-1). In general, normal hemoglobin levels are 1 to 2 grams/dL lower in women and black men than in white men.1 There are several classifications for anemia; based on pathophysiologic mechanisms, there are four main categories (Table 226-2).

Table 226-1 Normal Red Blood Cell Values for Adults
Table 226-2 Classification of Anemia

The body may respond to the development of anemia in several ways to blunt the effect of a reduction in oxygen-carrying capacity. These compensatory mechanisms vary, depending on the rapidity of onset, degree ...

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