Venous Blood gas tests are done to measure the levels of oxygen and carbon dioxide in your blood. The test also measures the balance of acids and bases in your blood caused by lactic acidosis or diabetic ketoacidosis. Venous Blood Gas test is done using blood from the vein. These tests are done if there is an injury that affects breathing, or you are having trouble breathing. It can also be done if you have acid building up in the body. This helps in assessing whether lungs and kidneys are working properly, and whether the blood has the right balance of acids and bases.