Published online: January 13, 2017
Chronic cough is a prevalent medical problem with a high degree of morbidity. Cough-variant asthma (CVA) and eosinophilic bronchitis (EB) are two common conditions underlying chronic cough worldwide, and their diagnostic approaches have been the integral part of international clinical guidelines for chronic cough. However, conventional tests for their diagnoses, such as methacholine challenge tests and induced sputum analyses, are technically demanding and therefore limited in their use to specialist centers. Fractional exhaled nitric oxide (FeNO), a recently developed biomarker for Th2 airway inflammation, has advantages of being a simple, rapid, and non-invasive test and thus has the potential to be widely used in clinical practice for chronic cough.
In a recent article published in The Journal of Allergy & Clinical Immunology (JACI), Song and colleagues examined the diagnostic accuracy of FeNO in predicting CVA and EB in adult patients with chronic cough. They performed a systematic review to summarize currently available evidence without language restriction and estimated the sensitivity and specificity of FeNO using a random effects meta-analysis model.
The authors identified 15 studies involving 2,187 adult patients. FeNO had a moderate diagnostic accuracy for predicting CVA in chronic cough population, showing the estimated area under the curve to be 0.87 (95% confidence interval [95% CI] 0.83–0.89). Optimal cut-off levels were mostly between 30 and 40 ppb. Notably, the overall specificity was higher and more consistent than sensitivity (0.85 [95% CI 0.81–0.88] and 0.72 [95% CI 0.61–0.81], respectively). Meanwhile, in non-asthmatic chronic cough population, FeNO showed a moderate accuracy to predict EB.
The findings suggest the diagnostic potential of FeNO as a ‘rule-in’ test for CVA, rather than a ‘rule-out’ test. As FeNO is a simple and non-invasive test, its integration into the diagnostic pathways for chronic cough may simplify diagnostic procedures for CVA and accelerate the treatment decision.
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.