Background The primary end-point in the management of asthma is to obtain optimal control. The aim of this study was to assess the relationships between the markers of airway inflammation (sputum eosinophilia and exhaled nitric oxide), bronchial hyperresponsiveness (BHR) and asthma control.
Methods One hundred and thirty-four patients were recruited from our asthma clinic between January 2004 and September 2005 [mean age: 42 years, mean forced expiratory volume in 1 s (FEV1): 86% predicted]. Eighty-six of them were treated by inhaled corticosteroids, 99 were atopic and 23 were current smokers. They all underwent detailed investigations including fractional-exhaled nitric oxide (FENO) measurement, sputum induction and methacholine challenge when FEV1 was >70% predicted, and filled in a validated asthma control questionnaire (ACQ6 Juniper).
Results When dividing patients into the three groups according to their level of asthma control determined by ACQ [well-controlled asthma (ACQ score 0.75), borderline (0.75<ACQ score <1.5) and uncontrolled asthma (ACQ score 1.5)], it appeared that uncontrolled asthmatics had a greater BHR to methacholine and sputum eosinophilia than controlled asthma (P<0.05, P<0.001, respectively). By contrast, we failed to show significant differences in the FENO levels between the groups. With receiver-operating characteristic curves for differentiating uncontrolled (ACQ1.5) from controlled and borderline (ACQ<1.5) asthma, sputum eosinophilia and methacholine responsiveness were found to be more accurate than FENO (area under the curve: 0.72, 0.72 and 0.59, respectively).
Conclusion In a broad spectrum of asthmatics encountered in clinical practice, sputum eosinophilia and methacholine bronchial hyperresponsiveness, but not FENO, are associated with uncontrolled asthma.