What condition is characterized by a decreased ability to carry oxygen in the blood?

Anemia is characterized by a decreased ability of the blood to carry oxygen, primarily due to a reduction in the number of red blood cells or a deficiency in the hemoglobin that they contain. Hemoglobin is the protein in red blood cells that binds to oxygen, so when there is insufficient hemoglobin or not enough red blood cells, the overall capacity of the blood to transport oxygen to the body tissues is diminished.

This condition can result from various factors, including nutritional deficiencies (like iron, vitamin B12, or folate), chronic diseases, or genetic disorders. Symptoms often include fatigue, weakness, and pale skin due to the body not receiving adequate oxygen.

In contrast, other conditions listed, such as leukemia, involve the proliferation of abnormal white blood cells but do not primarily impair the oxygen-carrying capacity. Thrombosis refers to the formation of a blood clot within a blood vessel, which can impede blood flow but doesn’t inherently affect the blood's ability to carry oxygen. Hypoxia refers to a state of reduced oxygen availability in tissues but is a consequence rather than a specific condition affecting blood capacity. Thus, anemia fits perfectly as the condition defined by decreased oxygen-carrying ability in the blood.