When the body exhales, it naturally releases some amount of nitric oxide gas. Often, people with asthma have higher levels. Inflammation is at the core of asthma. It affects the lining of the airway, which results in swelling and the overproduction of mucus and fluid. If you have asthma, you likely have certain triggers. Each time your airway is exposed to one, the inflammation in the lining can increase, causing noticeable symptoms. FeNO, fractional exhaled nitric oxide levels, occur because of this inflammation.
It's important to recognize that a FeNO test is not a complete diagnostic confirmation of asthma. What this test does is measure your levels of exhaled nitric oxide. It's therefore simply a measure of inflammation in the airway. It informs your doctor as they seek to understand the cause of your symptoms. If you've been diagnosed with asthma, the FeNO test can inform your doctor as they create a treatment plan to manage your condition.