Which statement correctly defines anemia?

• A. A reduction in the total circulating red cell mass below normal limits
• B. A decrease in white blood cell mass
• C. A decrease in plasma volume
• D. An increase in platelet count

Answer: (A)

Anemia is defined by a reduced total circulating red cell mass, meaning there are fewer erythrocytes in the bloodstream than normal, which lowers the oxygen-carrying capacity of the blood. Hemoglobin concentration and hematocrit are commonly used to diagnose anemia, but they can be influenced by plasma volume changes, so the fundamental concept is the decrease in circulating red cells themselves. A drop in white blood cells would be leukopenia, a change in plasma volume affects measurements but not specifically red cell mass, and an increased platelet count relates to thrombocytosis. Thus, the statement describing a reduction in the total circulating red cell mass below normal limits best captures the definition of anemia.