What is the condition in which blood has abnormally low oxygen-carrying capacity?

Anemia is defined as a condition where there is a deficiency in the number or quality of red blood cells, which leads to a reduced capacity of the blood to carry oxygen. This can occur due to various factors, such as a deficiency in iron, vitamin B12, or folate; chronic diseases; or bone marrow disorders. In anemia, the decrease in hemoglobin, the protein responsible for oxygen transport in red blood cells, directly contributes to the inadequate oxygenation of tissues, resulting in symptoms such as fatigue and weakness.

The other conditions mentioned do not primarily relate to the oxygen-carrying capacity of blood. Leukemia involves an overproduction of abnormal white blood cells and does not specifically impact red blood cell functionality in terms of oxygen transport. Cardiac tamponade refers to fluid accumulation in the pericardial space, which affects heart function but is not directly related to the oxygen-carrying capacity of blood. Myocardium refers to the heart muscle itself and is not a condition but rather a structure involved in pumping blood. Hence, anemia is distinctly characterized by its impact on oxygen-carrying capacity, making it the correct choice.