Friday, March 29, 2024

Anemia

Practice Essentials

Anemia is strictly defined as a decrease in red blood cell (RBC) mass. The function of the RBC is to deliver oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. This is accomplished by using hemoglobin (Hb), a tetramer protein composed of heme and globin. In anemia, a decrease in the number of RBCs transporting oxygen and carbon dioxide impairs the body’s ability for gas exchange.
The decrease may result from blood loss, increased destruction of RBCs (hemolysis), or decreased production of RBCs.

Anemia, like a fever, is a sign that requires investigation to determine the underlying etiology. Often, practicing physicians overlook mild anemia. This is similar to failing to seek the etiology of a fever. The purpose of this article is to provide a method of determining the etiology of an anemia. (See the image below.) (See Etiology, Presentation, and Workup.)

Microcytic anemia.

Microcytic anemia.

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Methods for measuring RBC mass are time consuming and expensive and usually require transfusion of radiolabeled erythrocytes. Thus, in practice, anemia is usually discovered and quantified by measurement of the RBC count, Hb concentration, and hematocrit (Hct). These values should be interpreted cautiously, because they are concentrations affected by changes in plasma volume. For example, dehydration elevates these values, and increased plasma volume in pregnancy can diminish them without affecting the RBC mass. (See Workup.)

Complications

The most serious complications of severe anemia arise from tissue hypoxia. Shock, hypotension, or coronary and pulmonary insufficiency can occur. This is more common in older individuals with underlying pulmonary and cardiovascular disease. (See Pathophysiology.)

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