FeNO Levels: What They Mean for Asthma and Airway Inflammation
When your doctor talks about FeNO levels, fractional exhaled nitric oxide, a biomarker that measures inflammation in the airways. It's a simple breath test that tells you how much nitric oxide is in your lungs — and that number can reveal if your asthma is flaring up, even before you feel it. High FeNO means your airways are swollen and irritated, often because of allergic triggers or uncontrolled inflammation. Low FeNO? That usually means your current treatment is working, or your symptoms might be caused by something else entirely.
This test isn’t just for asthma. It also helps doctors tell the difference between allergic asthma and other breathing problems like COPD or vocal cord dysfunction. Nitric oxide, a gas naturally produced by the body’s immune cells in the lungs rises when those cells are overactive — a sign your immune system is attacking your own airways. That’s why FeNO is so useful: it gives a real-time look at what’s happening inside, not just how you feel on a given day. And unlike blood tests or chest X-rays, it’s quick, safe, and doesn’t need needles or radiation.
FeNO levels change with treatment. If you’re on an inhaled steroid like fluticasone-salmeterol, your FeNO should drop over time — that’s a good sign. If it stays high, your doctor might adjust your dose or check if you’re using your inhaler right. Some people with asthma have normal lung function but high FeNO, meaning their inflammation is quietly ticking away. That’s why this test catches problems others miss.
It’s not perfect. FeNO can be affected by smoking, recent meals, or even recent exercise. But when used right — and paired with your symptoms and lung function tests — it becomes a powerful tool. Airway inflammation, the hidden driver behind wheezing, coughing, and shortness of breath doesn’t always show up on a stethoscope. FeNO makes it visible.
Below, you’ll find real-world guides on how this test fits into daily asthma care, how it connects to medication choices, and what to do when results don’t match how you feel. Whether you’re managing your own asthma or helping someone else, these posts give you the facts you need — no jargon, no fluff, just what works.
