Which medical condition results from a lack of red blood cells leading to fatigue?

Anemia is a medical condition characterized by a deficiency in the number of red blood cells or hemoglobin in the blood, which is crucial for transporting oxygen throughout the body. When there aren’t enough healthy red blood cells, the body does not receive adequate oxygen, leading to symptoms such as fatigue, weakness, and reduced physical performance. This condition directly correlates with the symptoms described in the question, making it the correct choice.

In contrast, leukemia is a type of cancer that affects the blood and bone marrow, leading to the production of abnormal white blood cells, and while it can cause fatigue, it involves a more complex pathology than simply a reduction in red blood cells. Hemophilia is a genetic disorder that impairs the body's ability to make blood clots, which can lead to excessive bleeding but is not primarily related to red blood cell count. Thrombocytopenia refers to a low platelet count, which affects clotting rather than oxygen transport and can also lead to bleeding, but does not directly result in the lack of red blood cells or fatigue related to oxygen deficiency.