The value of exhaled nitric oxide to identify asthma in smoking patients with asthma-like symptoms

Respiratory Medicine 2012, 106(6), 794-901
Andrei Malinovschi, Vibeke Backer, Henrik Harving, Celeste Porsbjerg

報告者：戴淑婷 102.07

Background

The fraction of nitric oxide in exhaled air (FeNO) is used in asthma diagnosis and management. Smoking reduces FeNO and 20–35% of asthmatics are smoking. However no guidelines exist on the diagnostic value of FeNO in smokers. Therefore we assessed the value of FeNO to diagnose asthma in a population of subjects with asthma-like symptoms and different smoking habits.

Methods

Measurements of FeNO, lung function, bronchial responsiveness and allergy testing were performed in 282 subjects (108 never-, 62 ex- and 112 current smokers) aged 14–44 years, with symptoms suggestive of asthma. These subjects were a subset of subjects reporting respiratory symptoms (n = 686) in a random population sample (n = 10,400).

Results

A diagnosis of asthma was given to 96 of the 282 subjects. Subjects with asthma had higher FeNO levels than subjects with non-specific asthma symptoms in all three smoking strata (p < 0.001), with a percentual increase of FeNO by 76% in never-, 71% in ex- and 60% in current smokers. The area under the ROC-curve was similar in never-, ex- and current smokers (0.72 vs. 0.74 vs. 0.70). The cut-offs were approximately 30% lower for either 90% specificity (22 vs. 31 ppb) or 90% sensitivity (7 vs. 10 ppb) in current vs. never-smokers.

Conclusions

FeNO could differentiate asthmatic subjects from non-asthmatic subjects with asthma-like symptoms equally well in both never- and current smokers within a random population sample. The FeNO cut-off levels needed in order to achieve high sensitivity or specificity were lower in current smokers.