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Table 1 Categorisation of FeNO level - low/normal; intermediate; high by age (i.e. adults and children)

From: Using fractional exhaled nitric oxide (FeNO) to diagnose steroid-responsive disease and guide asthma management in routine care

  Adults/Adolescents (Ages 12 and older) Children (Ages 4–11)
Low/normal (ppb) <25 <20
Intermediate (ppb) ≥25 and ≤50 ≥20 and ≤35
High (ppb) >50 >35
  1. Normal FeNO level = <25 ppb/<20 ppb in patients age ≥12/< 12 years. Intermediate FeNO level = 25–50 ppb/20-35 ppb in patients age ≥12/< 12 years. High FeNO level = >50 ppb/>35 ppb in patients age ≥12/< 12 years.