Arterial blood gas analysis is a test that measures how much oxygen and carbon dioxide is in the blood. It also determines the acidity (pH) of the blood. Typically blood is collected from the radial artery in the wrist, the femoral artery in the groin or the brachial artery in the arm. It is helpful in evaluating respiratory diseases and conditions that affect the lungs. It also helps determine the effectiveness of oxygen therapy and provides information about the body’s acid/base balance. Ph results can reveal important clues about lung and kidney function and the body’s general metabolic state.