Lung diffusion testing is used to determine how well oxygen passes from the air sacs of the lungs into the blood. The test measures the "diffusing capacity of the lung for carbon monoxide" or DLCO.

You breath in (inhale) some gas containing a very small quantity of carbon monoxide, hold your breath for 10 seconds, then rapidly blow it out (exhale). The single exhaled gas is analyzed to determine how much carbon monoxide was absorbed during the breath.

Do not eat a heavy meal before the test. Do not smoke for at least 4 - 6 hours prior to the test. If you use a bronchodilator or inhaler medications, ask your health care provider whether or not you can use them before the test.

The mouth piece fits tightly around your mouth. Clips are put on the nose. 

The test is used to diagnose the presence and extent of certain lung diseases. It may also be used to see how gases move the lungs into the bloodstream.

Normal test results depend on a person's age, sex, and height.

Abnormal results generally mean that gases do not move normally across the lung tissues. This may mean that lung diseases, such as interstitial fibrosis, sarcoidosis, asbestosis, and emphysema, are present.

There are no significant risks.

Other pulmonary function tests may be done in combination with this test.

Lamberto C, Nunes H, Le Toumelin P, Duperron F, Valeyre D, Clerici C. Membrane and capillary blood components of diffusion capacity of the lung for carbon monoxide in pulmonary sarcoidosis: relation to exercise gas exchange. Chest. 2004 Jun;125(6):2061-8.

Mohsenifar Z, Lee SM, Diaz P, et al. Single-Breath Diffusing Capacity of the Lung for Carbon Monoxide: A Predictor of PaO2, Maximum Work Rate, and Walking Distance in Patients With Emphysema. Chest 123: 1394-1400.