A blood gas test is done to measure the amount of O2 & CO2 in the blood. It is also be used to determine the pH of the blood(alkaline or acidic).The test is commonly known as a blood gas analysis or ABS test.The RBCs transport O2 and CO2 throughout the body. These are the blood gases. The blood gas test can be used to find how your lungs are functioning i.e, moving O2 and removing CO2 from the blood. Imbalances in the O2, CO2, and pH levels of the blood are the indication of some medical conditions.