Lung diffusion testing measures how well the lungs exchange gases. This is an important part of lung testing, because the major function of the lungs is to allow oxygen to "diffuse" or pass into the blood from the lungs, and to allow carbon dioxide to "diffuse" from the blood into the lungs.
How the Test is Performed
You breathe in (inhale) air containing a very small amount of a tracer gas, such as carbon monoxide. You hold your breath for 10 seconds, then rapidly blow it out (exhale). The exhaled gas is tested to determine how much of the tracer gas was absorbed during the breath.
How to Prepare for the Test
- Do not eat a heavy meal before the test.
- Do not smoke for at least 4 - 6 hours before 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.
How the Test will Feel
The mouthpiece fits tightly around your mouth. Clips are put on your nose.
Why the Test is Performed
The test is used to diagnose certain lung diseases, and to monitor the status of people with established lung disease. Repeatedly measuring the diffusing capacity can help determine whether the disease is improving or getting worse.
Normal test results depend on a person's:
- Hemoglobin (the protein in red blood cells that carries oxygen) level
What Abnormal Results Mean
There are no significant risks.
Other pulmonary function tests may be done together with this test.
Diffusing capacity; DLCO test
Hegewald MJ, Crapo RO. Pulmonary function testing. In: Mason RJ, Broaddus VC, Martin TR, et al., eds. Murray and Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, Pa: Elsevier Saunders; 2010:chap 24.
Reynolds HY. Respiratory structure and function: mechanisms and testing. In: Goldman L, Schafter AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 85.
Update Date 12/3/2013
Updated by: Denis Hadjiliadis, MD, Associate Professor of Medicine, Pulmonary, Allergy, and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pa. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.