NO concentration in exhaled breath is measured in “parts per billion” (ppb). That is roughly equivalent to five brown blades of grass on an entire soccer field.
According to scientific findings, normal FeNO values depend, among other things, on height and gender.
- Women usually have lower values than men
- Children lower values than adults
As a guide:
- Values below 25 ppb are considered normal (children below 20 ppb) and
- Values above 50 ppb (children above 35 ppb) indicate active inflammation of the airways.
The American Thoracic Society (ATS), based in New York, is a leading international society in the field of respiratory disease, critical illness, and sleep disorders. Their guideline states that values between 0 and 25 ppb are low, between 25 and 50 ppb are in the mid-range and above 50 ppb are high
The renowned British National Institute for Health and Care Excellence (NICE) also publishes guidelines for the application of treatments and procedures. The current Asthma Directive states that FeNO values above 40 ppb in adults (above 35 ppb in children) are high.
In general, your doctor makes the diagnosis and decides on a therapy plan based on reference values.