What condition is characterized by a low red blood cell (RBC) count?

Anemia is defined by a decrease in the number of red blood cells (RBCs) or a low hemoglobin concentration within those cells. This condition can arise from various factors, including inadequate production of RBCs, increased destruction, or blood loss. Symptoms of anemia often include fatigue, weakness, and pallor, as the reduced RBCs lead to decreased oxygen transport to tissues.

In contrast, polycythemia is characterized by an increased number of RBCs, which means it is the opposite of anemia. Thrombocytopenia refers to a low platelet count, affecting blood clotting and not the RBC count. Leukopenia involves a decreased white blood cell count, which impacts the immune response rather than red blood cells. Thus, anemia is the only option that directly correlates with a low RBC count, supporting the correctness of this choice.