FeNO Testing: What It Is and How It Helps Manage Asthma and Airway Inflammation

When your lungs feel tight, you’re coughing at night, or inhalers aren’t doing enough, FeNO testing, a simple breath test that measures nitric oxide levels in your airways to detect inflammation. Also known as fractional exhaled nitric oxide testing, it’s a non-invasive way to see if your asthma is driven by allergic inflammation—not just symptoms. Unlike chest X-rays or lung function tests that show how well you’re breathing right now, FeNO testing shows why you’re having trouble breathing. It tells your doctor if the inside of your airways is swollen and irritated, which is often the hidden cause of flare-ups.

This test matters because not all asthma is the same. Some people have inflammation caused by allergies, others by smoke or stress. If your FeNO levels are high, it means your body is producing excess nitric oxide as a signal of that inflammation—and that’s when inhaled corticosteroids are most likely to help. If levels are normal, your doctor might look elsewhere: acid reflux, vocal cord issues, or even heart problems. That’s why FeNO testing isn’t just another lab number; it’s a guide to choosing the right treatment. It also helps track if your meds are working. A drop in FeNO after starting a steroid inhaler? That’s proof it’s reducing inflammation. A rise after skipping doses? That’s your body warning you a flare-up is coming.

FeNO testing is quick, safe, and done in minutes at your doctor’s office. You breathe steadily into a handheld device—no needles, no fasting, no discomfort. Kids as young as 5 can do it. It’s especially useful if you’re not responding to standard asthma meds, if your symptoms don’t match your lung test results, or if you’re trying to cut back on steroids and need to know if it’s safe. It’s also used to monitor chronic coughs that don’t go away, since persistent inflammation is often the root cause.

Behind the scenes, FeNO testing connects to other key areas of respiratory care. It relates to inhaled corticosteroids, the most common long-term asthma control medication that reduces airway swelling, because it shows whether those drugs are actually doing their job. It ties into allergic rhinitis, a condition often linked to asthma where nasal inflammation signals broader airway issues—many people with high FeNO also have runny noses and sneezing. And it’s part of a bigger picture that includes asthma diagnosis, the process of confirming asthma through symptoms, tests, and response to treatment, helping avoid misdiagnosis like COPD or vocal cord dysfunction.

What you’ll find in the posts below isn’t just theory. Real cases. Real results. From how a teen’s FeNO levels dropped after switching inhalers, to why a smoker’s test came back normal despite wheezing, to how one doctor uses FeNO to avoid unnecessary antibiotics. These aren’t abstract studies—they’re stories from people who’ve been there. You’ll learn how to talk to your doctor about this test, what the numbers actually mean, and how to use them to take control of your breathing—not just treat the symptoms.