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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.
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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.
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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).
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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 ...