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ACAAI > Patients & Public > Resources > Ask the Allergist

What is Nitric Oxide Testing?

Q. Recently, my child visited his allergist because of seasonal nasal allergy symptoms mixed with cough and wheezing. During the visit, the allergist recommended a breathing test called “FeNO” and explained that my insurance may not cover the cost. What is “FeNO” and do you feel its value outweighs its cost?

A. FeNO stands for “Fractional exhaled Nitric Oxide.” Nitric oxide* is an objective biomarker of inflammation in the lungs. (A biomarker is a chemical byproduct of a natural process in the body that can be measured.) Your doctor ordered this important test to determine if your child’s symptoms were caused by asthma or something else -nitric oxide testing helps to determine this. Higher levels are associated with more inflammation, and likelihood of asthma. Many diseases have symptoms similar to those seen in asthma. Understanding whether airway inflammation is present can help rule out these other conditions and support a diagnosis of asthma.

Inflammation is the underlying cause of asthma and this inflammation is what causes clinical symptoms. Traditional methods of asthma assessment only tell part of the story and are indirectly associated with airway inflammation. Nitric oxide testing predicts the likelihood of steroid response in an individual and helps the physician get to the right treatment decision quickly. Many view nitric oxide as a "vital sign" for asthma just like blood pressure is, in a patient with high blood pressure. Nitric oxide is a valuable monitoring tool, and can help to determine if a person with asthma can safely taper medication. This test is not yet covered by all insurances and varies greatly from state to state. In my opinion, the value of nitric oxide testing certainly outweighs the upfront cost for two important reasons:

1. Helps determine if a person will respond to steroids before paying the co-pay for a "trial" dose.
2. Helps a person stay on needed medication, as they see the medicine is working to decrease the nitric oxide level (vital sign). With asthma symptoms under control, a person will spend less time and money in doctors' offices and in taking extra medication.

*Note: Nitric oxide should not be confused with nitrous oxide, also known as "laughing gas", used as a general anesthetic such as for dental procedures.