Exhaled nitric oxide as a diagnostic test for asthma in rhinitic patients with asthmatic symptoms

Summary

Background

Rhinitis is a major risk factor for asthma, so that evaluation of the lower airways is recommended in patients with rhinitis. Exhaled nitric oxide (FE_NO) is considered a marker of airway inflammation and it has been found to be useful for the screening of patients with suspected diagnosis of asthma. Our aim was to assess the validity and accuracy of FE_NO to identify patients with asthma in 48 non-smoking patients with persistent rhinitis and asthma-like symptoms.

Methods

Asthma was diagnosed on the basis of 12% improvement in FEV₁ after salbutamol or a methocholine PD₂₀FEV₁<800 μg. Prior to lung function FE_NO was measured with the single exhalation method at 50 ml/s.

Results

The geometric mean (95% confidence interval) FE_NO was significantly higher in the 18/48 asthmatics than in the non-asthmatic patients (60 ppb, CI 95%: 50–89, versus 30 ppb, CI 95%: 28–45, $P=0.001$). Receiver operating characteristic (ROC) curve for the diagnosis of asthma indicated that FE_NO is an acceptable discriminator between patients with and without asthma (area under the ROC curve=0.78). None of the asthmatic patients had FE_NO values<25 ppb and all the patients with FE_NO>100 ppb ($n=5$) were asthmatics. The sensitivity and specificity of FE_NO for detecting asthma, using 36 ppb as cut-off point, were 78% and 60% and the positive and negative predictive values were 54% and 82%, respectively.

Conclusions

Measuring FE_NO may be useful for the screening of rhinitic patients with asthma-like symptoms.