What condition refers to a low oxygen level in the blood?

The condition that refers to a low oxygen level in the blood is hypoxemia. It specifically describes insufficient oxygen in arterial blood, often assessed through oxygen partial pressure, oxygen content, or hemoglobin saturation.

Hypoxemia commonly results from problems affecting breathing or oxygen transfer in the lungs. Causes can include lung disease, inadequate ventilation, impaired diffusion, ventilation–perfusion mismatch, shunting, or reduced oxygen availability at high altitude.

Hypoxia is related but broader: it means inadequate oxygen at the tissue or whole-body level. Hypoxemia can cause hypoxia, but tissue oxygen deficiency may also occur despite normal blood oxygen—for example, when blood flow is severely reduced or tissues cannot use oxygen properly. Therefore, hypoxemia is the most precise answer for low oxygen specifically in the blood.