Even though an inflammatory process is known to be the underlying cause of asthma, diagnosis is based on clinical history, reversible airway obstruction and bronchial hyperresponsiveness according to international guidelines. The fraction of exhaled nitric oxide (FENO) and induced sputum eosinophil count (Eos%) have been used as non-invasive inflammatory biomarkers.
Objectives
The aim of this study was to compare the sensitivity and specificity of FENO, Eos% and spirometry and to assess whether their combined use in clinical practice would improve diagnostic yield.
Methods
In 50 patients with asthma symptoms we performed spirometry, a methacholine challenge test, FENO measurement and assessment of Eos% in induced sputum. The standard diagnosis of asthma followed the guidelines of the Global Initiative for Asthma.
Results
Twenty-two of the 50 patients were diagnosed with asthma. The sensitivity and diagnostic accuracy were higher for FENO measurement (77%; area under the receiver operating curve [AUC], 0.8) than for spirometry (22%; AUC, 0.63). The sensitivity and specificity of Eos% in induced sputum were 40% and 82%, respectively, and the diagnostic accuracy of Eos% was lower (AUC, 0.58). When both inflammatory biomarkers were used together specificity increased to 76%.
Conclusions
The diagnostic accuracy of FENO measurement was superior to that of the standard diagnostic spirometry in patients with symptoms suggestive of asthma. The use of FENO measurement and induced sputum Eos% together to diagnose asthma in clinical practice is more accurate than spirometry or FENO assessment alone and easier to perform.
Abbreviations
FENO
fraction of exhaled nitric oxide
Eos%
eosinophil count expressed as a percentage
PPV
positive predictive value
NPV
negative predictive value
FEV1
forced expiratory volume in 1 s
FVC
forced vital capacity
ppb
parts per billion
PD20
the dose of methacholine producing a 20% fall in FEV1
ROC
receiver operating characteristic curve
AUC
area under the receiver operating characteristic curve