Exhaled nitric oxide has been studied since 1991 and several studies have shown it to be powerful tool in management of asthma. The American Thoracic Society (ATS) and European Respiratory Society (ERS) have jointly published guidelines for the standardized measurement of eNO.1 Recent asthma guidelines (NHLBI) indicate the positive role of inflammation measurements, of which eNO is the most clinically viable.

The clinical utility of measuring eNO include:

1. Selecting and Titrating Medication

Exhaled nitric oxide has been shown to predict the likelihood of a steroid response more consistently than spirometry or bronchodilator response.2 Use of eNO to direct inhaled steroid therapy was shown to reduce dosage while maintaining asthma control.3

2. Monitoring Compliance

An elevated eNO is suggestive of inadequate anti-inflammatory therapy – either from an insufficient dose or due to patient non-compliance.4 Reduction of exhaled NO levels after the start of therapy can reassure a physician that the treatment regime is being followed, and can demonstrate to the patient the physiological change that the therapy could achieve if properly followed.5

3. Predicting Exacerbation and Loss of Control

The ability to predict a worsening of symptoms is the most exciting clinical application of eNO measurement. Exhaled nitric oxide is a better predictor over FEV1 of both asthma control, loss of control and worsening of asthma.6 Elevated eNO measured at a clinic visit indicates increased risk of an exacerbation occurring within the next two weeks.7 Pediatric studies have found that an eNO level above 47 ppb predicts loss of control when inhaled steroids are reduced or withdrawn.8 A rise in eNO among patients who cease steroid therapy is predictive of an upcoming relapse.9 A home monitoring study showed that frequent eNO measurements may have predictive power for impending instability of asthma.10,11

Last edited by Kate; 07/28/09 03:08 PM.