A 45-year-old man presents to the physician with a sore throat and fever for the past 3 days. of three days' duration. He also reports dyspnea on exertion and fatigue for the past three months and states that these have worsened over this time. Past medical history is unremarkable, and he does not take any prescription medications. Physical examination reveals tachycardia and scattered ecchymoses over the arms and legs.
Which of the following laboratory values would best illustrate the patient's red blood cell count?
A) Hematocrit
Of the options, only hematocrit gives an accurate measure of the red blood cell (RBC) count. Hematocrit is the percentage of blood volume occupied by RBCs. Mean corpuscular hemoglobin concentration (MCHC) is the average hemoglobin concentration per RBC.
Mean corpuscular volume (MCV) is the average volume (size) of the RBCs.
Red cell distribution width (RDW) is a measure of the variation in RBC size, which is reflected in the degree of anisocytosis on the peripheral blood smear.
Total iron binding capacity (TIBC) measures the total amount of iron that can be bound by proteins in the blood. Since transferrin is the primary iron-binding protein, the TIBC is an indirect measurement of transferrin availability.
Key Learning Point
Hematocrit is the percentage of blood volume occupied by red blood cells. Hemoglobin is the protein contained in red blood cells that is responsible for delivery of oxygen to the tissues and is reported as the concentration of hemoglobin in whole blood.
