Exhaled Nitric Oxide Test

Last Updated 05/07/2020

Authors:Rubin Cohen, MD, FCCP; Melissa Lesko, DO, BA; Malvika Sagar, MBBS

About the Exhaled Nitric Oxide Test

Key facts about this test

An exhaled nitric oxide level test can help diagnose and manage asthma. It measures the amount of nitric oxide exhaled with each breath. High levels of nitric oxide in the breath may mean that the lung airways are swollen. This test can be used to find out whether someone with asthma is helped by certain medications.

What to expect

How is the test done?

The exhaled nitric oxide test is similar to a pulmonary function test, also called spirometry. A member of your health care team helps and guides you. The test takes less than 5 minutes to complete.

You will be asked to:

  • Put clips on your nose.
  • Exhale, or breathe out, and completely empty your lungs.
  • Put the mouthpiece in your mouth. Then, breathe in slowly and deeply to fill your lungs with air.
  • Exhale slowly and steadily until you hear a beep or a light comes on. Your health care provider may have you watch a computer monitor. On this screen, it shows how much you’re breathing out so that you can breathe out steadily.

You may need to repeat the test to confirm your results.

Understanding the results

What do the results mean?

A level of nitric oxide that is higher than normal means that there is swelling, called inflammation, in the lining of the airways. It could also mean that you have allergic asthma. This swelling can often be managed with medications called corticosteroids.

The test results are used to decide or show:

  • Whether you should take steroid medications to manage your asthma;
  • How effective your medications are if you are already taking steroids;
  • Whether you are following your asthma treatment plan; and
  • Whether you should modify your therapy plan. You may be asked to do the test 3 to 4 times a year.

In some cases, the results are used to diagnose asthma. The test results are used with the results of other diagnostic tests.

What are the risks?

Is this test safe?

This test is quick and safe. Rarely, some people might feel lightheaded when they are asked to breathe out and breathe in. In this case, the provider will ask you to sit and relax for a few minutes. Then, you can try the test again.