What is the normal range for nitric oxide exhalation test results?

Patient's question:

What is the normal range for nitric oxide exhalation test values? For asthma testing in 12-year-old children

Doctor's answer:

Guidance: The normal reference value is (20-60)×10-9 (20-60 ppb). If there is a problem detected in this general test, it is important to start treatment promptly. Doctor's inquiry: