What are the defining features of aplastic anemia?

• A. Pancytopenia with hypocellular bone marrow; decreased RBCs, WBCs, and platelets; increased infection and bleeding risk
• B. Elevated RBCs and WBCs with hypercellular marrow
• C. Isolated anemia with normal WBCs and platelets
• D. Pancytopenia with hypercellular marrow

Answer: (A)

Aplastic anemia is characterized by a failure of the bone marrow to produce blood cells, leading to pancytopenia and a hypocellular marrow. Pancytopenia means all three blood cell lines are reduced—red blood cells (causing fatigue and pallor), white blood cells (increasing infection risk), and platelets (increasing bleeding risk). The bone marrow biopsy in this condition shows a markedly hypocellular marrow with fat replacement and very few hematopoietic precursors, not a hypercellular, crowded marrow. This combination distinguishes it from conditions with normal or elevated cell production or from isolated anemia.