Diffusion capacity is used to evaluate the diffusibility of gases or ease with which gases pass through the lung membranes and are absorbed into the body. This test measures your lung’s efficiency of delivering oxygen and other gases to your bloodstream. A number of physiological and pathological states can affect the diffusioning capacity including asthma, lung restriction, being exposed to chemotherapy agents, pulmonary hemorrhage, fibrosis etc. Like spirometry, this test is done by having the patient breathe into a mouthpiece connected to a machine. You will be asked to empty your lungs by gently breathing out as much air as you can. Then you will breathe in a quick but deep breath, hold your breath for 10 seconds, and then breathe out as instructed.