A normal FeNO depends on age: in adults, values under about 25 parts per billion (ppb) are considered low/normal, 25–50 ppb is intermediate/elevated, and above 50 ppb is high. In children, under ~20 ppb is normal, 20–35 ppb intermediate, and >35 ppb high. Smoking and recent steroid use can lower FeNO; interpret with clinical context.

FeNO (fractional exhaled nitric oxide) is a noninvasive breath test measuring nitric oxide levels in parts per billion, reflecting eosinophilic airway inflammation. It helps diagnose and monitor asthma, predict corticosteroid responsiveness, and guide treatment adjustments. Elevated FeNO suggests active airway inflammation; low levels make eosinophilic inflammation less likely. The test is quick, repeatable, and complements clinical assessment and lung function tests.

A high FeNO indicates eosinophilic (type 2) airway inflammation and commonly points to allergic or eosinophilic asthma. It predicts likely responsiveness to inhaled corticosteroids and usually prompts treatment review—starting or increasing steroids, checking adherence and inhaler technique, and reassessing control with further tests (spirometry). Other contributors (recent allergen exposure, atopy) should also be considered.

A FeNO (fractional exhaled nitric oxide) test is non-invasive and generally painless. You simply breathe into a mouthpiece for a few seconds; it may require several controlled breaths but involves no needles or injections. It’s quick, safe, and well tolerated by adults and children. Some people may find breath-holding or repeated attempts mildly uncomfortable, but significant pain is not expected.

Type 2 asthma is a form of asthma driven by type 2 immune inflammation—mainly Th2 cells and cytokines IL‑4, IL‑5 and IL‑13. It features eosinophilic airway inflammation, often elevated IgE and allergic triggers, and commonly responds to inhaled corticosteroids and targeted biologic treatments (anti‑IL‑5, anti‑IL‑4/13). Symptoms include wheeze, cough and breathlessness, with variable severity and exacerbations.

FeNO testing costs vary by country and setting. In the US private clinics or labs typically charge about $40–$200 (insurance may cover some or all). In the UK it’s free on the NHS where offered, while private clinics charge roughly £40–£90. In India prices generally range around ₹1,000–₹4,000. Actual out‑of‑pocket cost depends on local providers and insurance coverage.