What medical condition is characterized by decreased oxygen levels in the blood?

The medical condition characterized by decreased oxygen levels in the blood is hypoxemia. Hypoxemia specifically refers to an inadequate concentration of oxygen in the bloodstream, which can lead to various health issues affecting organ function and overall physiological stability. This condition can arise from several underlying causes, such as respiratory diseases (like chronic obstructive pulmonary disease or pneumonia), congenital heart defects, or altitude-related issues, where the proportion of oxygen available in the lungs is insufficient for normal saturation of hemoglobin.

In contrast, hypertension relates to elevated blood pressure, hyperventilation refers to an increased rate of breathing often leading to carbon dioxide imbalance, and hematocrit measures the proportion of blood volume that is occupied by red blood cells, which does not directly address oxygen levels in the blood. Thus, hypoxemia directly represents a deficit in oxygen, making it the most accurate choice in this context.