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Kurs: MCAT > Rozdział 2

Lekcja 1: Biological sciences practice passage questions

A clinical approach to anemia: solve the case


A homeless patient in the ER is found to have dry, cracked lips and symptoms of severe anemia. Bloodwork was done, and found to be the following:
Hgb: 15g/dL; Hct: 45%; Absolute retic: 89,000; MCV: 78fL/cell
Anemia is a relatively common symptom of numerous medical conditions. The clinical findings in an anemic patient are associated with decreased or insufficient oxygen delivery to the tissues, known as hypoxia. Anemia is defined as a decrease in the total red blood cell (RBC) mass in an individual, though this definition is of little clinical use. Instead, clinicians rely on several other measures to identify the degree and the cause of anemia in a given patient (Table 1).
Table 1: Diagnostic blood measurements.
The cause of anemia can be broken down into two broad categories: a decrease in the number of RBCs, or a decrease in functional hemoglobin. The latter is easily measured by the total hemoglobin concentration. The number of RBCs can be determined either as an absolute count of circulating cells per volume, or as a measure known as the hematocrit. The hematocrit describes the proportion of whole blood that is made up of red cells. Though important, these measures are not always sufficient to identify an anemic patient.
Anemias can also be differentiated in mechanistic terms—is the decreased hematocrit/hemoglobin due to decreased production, or to increased destruction or loss? The reticulocyte count, a quantitative measure of the concentration of immature RBC precursors in circulation, can make this distinction. If the anemia is due to decreased production, the reticulocyte count is inappropriately low.
The mean corpuscular volume (MCV) describes the average volume of circulating RBCs. A low MCV, referred to as a microcytic anemia usually results from decreased hemoglobin; a decrease in hemoglobin usually results from an iron deficiency. A normocytic anemia may be due to a condition known as aplastic anemia, wherein the stem cell precursors to all blood components—RBCs, leukocytes, and platelets—are damaged. This results in a global decrease in these cells, though they appear normal. The diagnostic algorithm described in the passage is summarized in Figure 1.
Figure 1: Diagnostic algorithm for determining the cause of anemia.
In what context might an anemic patient’s hematocrit and hemoglobin concentration both appear to be normal or elevated?
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