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By Mayo Clinic staff
For a nitric oxide test, your doctor will have you breathe into a mouthpiece attached to a machine that measures nitric oxide levels in your breath. You will get specific instructions on how and when to breathe to make sure your test results are accurate.
Your doctor will probably ask you detailed questions about any asthma signs and symptoms you've been having. Your doctor will also likely give you lung function tests, which measure how quickly you can exhale and how much air you can exhale.
During the test
To do this test, you'll be seated. Your doctor will have you put in a mouthpiece attached to an electronic measurement device with a computer monitor. Next, you'll breathe in for two or three seconds until your lungs are filled with air. Your doctor will then have you exhale steadily so that the air flows out of your lungs at an even rate. Your doctor may have you watch a computer monitor that registers how much you are breathing out so that you can maintain a steady exhalation. You'll need to repeat the test a few times to confirm your results. The entire test generally takes five minutes or less.
Nitric oxide test results are immediately available, but your doctor may need to consider other factors, such as the results of lung function tests, to accurately evaluate your signs and symptoms of asthma.
In some cases, your doctor may give you a portable device to measure your nitric oxide levels at home. This record will help you and your doctor monitor your asthma symptoms on a daily basis.
After the test
The results of a nitric oxide test are immediately available. Your doctor will use this information to help diagnose or evaluate asthma, along with any other test results and your answers to questions about your symptoms. If you have asthma, your doctor will use this information to help guide decisions about your medications and other steps you need to take to manage your asthma.
Your doctor may test you, and then give you inhaled asthma medications to see if your nitric oxide levels go down. This can help your doctor judge whether treatment improves your airway inflammation.
- Stewart L. Exhaled nitric oxide. Immunology and Allergy Clinics of North America. 2007;27:571.
- American Thoracic Society. ATS/ERS recommendations for standardized procedures for the online and offline measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005. American Journal of Respiratory and Critical Care Medicine. 2005;171:912.
