What does anemia refer to?

Anemia refers to a condition characterized by a decrease in the number of red blood cells, a crucial component of the blood that is responsible for transporting oxygen throughout the body. When there are fewer red blood cells than normal, the body may not receive adequate oxygen, which can lead to a variety of symptoms, including fatigue, weakness, and paleness.

The other options describe different medical conditions that do not define anemia. For example, conditions caused by parasites would involve infections or infestations that affect health but do not specifically relate to the quantity of red blood cells. An increase in white blood cells is associated with infections or inflammation, which is out of context for anemia's definition. Additionally, respiratory conditions pertain to issues with the lungs or breathing and do not impact the red blood cell count in the same manner anemia does. Thus, the primary defining characteristic of anemia remains the decrease in red blood cells.