A normal fractional exhaled nitric oxide (FeNO) is generally under 25 parts per billion (ppb) in adults and under 20 ppb in children. Values between 25–50 ppb (adults) or 20–35 ppb (children) are intermediate, while >50 ppb (adults) or >35 ppb (children) suggest significant eosinophilic airway inflammation and likely steroid responsiveness. Interpretation depends on clinical context.

Fractional exhaled nitric oxide (FeNO) is a noninvasive breath test measuring nitric oxide concentration in exhaled air, reported in parts per billion (ppb). FeNO indicates eosinophilic airway inflammation and aids asthma diagnosis, monitoring, and predicting steroid responsiveness. Typical adult thresholds: <25 ppb low, 25–50 ppb intermediate, and >50 ppb suggesting significant eosinophilic inflammation.

A high FeNO (fractional exhaled nitric oxide) indicates airway eosinophilic inflammation, often seen in allergic or steroid‑responsive asthma. It suggests poorer asthma control and a higher risk of exacerbations. Clinicians may use a high FeNO to justify starting or increasing inhaled corticosteroids, review adherence, consider allergy testing, and order further lung function tests to guide treatment and monitoring.

The cost of a FeNO (fractional exhaled nitric oxide) test varies widely. On public health systems it’s often free; privately it ranges roughly Rs 700–3,000 in India, about £30–£100 in the UK, and roughly $40–$200 in the US. Exact price depends on clinic, device, and insurance coverage—ask your provider or billing office for local pricing.

Fractional exhaled nitric oxide (FeNO) measures airway nitric oxide and indicates eosinophilic airway inflammation often seen in asthma. Elevated FeNO suggests active eosinophilic inflammation and likely corticosteroid responsiveness; low FeNO makes eosinophilic asthma less likely. Common adult cut-offs: <25 ppb low, 25–50 ppb intermediate, >50 ppb high. Interpret alongside symptoms, spirometry and clinical history.

Eosinophilic asthma is caused by an overactive immune response that drives high eosinophil levels in the airways. Type 2 inflammation—mediated by cytokines such as IL‑5, IL‑4 and IL‑13—recruits eosinophils. Triggers include allergies, viral infections, pollutants, smoking, certain medications, and underlying conditions like chronic rhinosinusitis with nasal polyps. Genetics and adult-onset immune dysregulation also increase risk.