In the context of an overview of host defenses, what is a differential white blood cell (WBC) count?

• A. A laboratory test that reports the relative proportions (percentages) of different leukocyte types (e.g., neutrophils, lymphocytes, monocytes, eosinophils, basophils) in a blood sample
• B. A laboratory test that determines the plasma concentration of antibodies (immunoglobulins) against a specific antigen
• C. A laboratory test that measures the total number of red blood cells per unit volume of blood
• D. A laboratory test that measures platelet function by assessing clotting time in whole blood

Answer: (A)