FeNO threshold values depend, among other things, on height and gender; women have lower values than men, children lower values than adults. The guidelines of the American Thoracic Society (ATS) state that values between 0 and 25 ppb are low, between 25 and 50 ppb medium and above 50 ppb high. As a guide, values below 25 ppb can be considered normal (children below 20 ppb). Values above 50 ppb (children above 35 ppb) indicate active inflammation of the respiratory tract. However, the final diagnosis is up to the doctor, who makes the diagnosis based on known reference values. Since these can vary from country to country, we refrain from storing the reference values, especially with the Vivatmo pro device for physicians.