Arterial blood gas (ABG) analysis is a test that measures oxygen and carbon dioxide levels in the blood and how well the lungs and kidneys are functioning. An ABG test requires drawing an arterial blood sample, usually from the wrist, to analyze pH, pCO2, pO2, HCO3, and O2 saturation levels. The results can help diagnose conditions that affect breathing or the lungs like COPD, pneumonia, or pulmonary embolism.