Noninvasive assessment of airway inflammation in children: induced sputum, exhaled nitric oxide, and breath condensate.

Noninvasive markers of airway inflammation are needed for use in research and clinical practice in childhood asthma. Induced sputum and exhaled nitric oxide are well established as direct markers of inflammation for use in asthma research. Sputum can be induced from children of >6 yrs using inhalation of hypertonic saline, and, if appropriate, can be combined with an assessment of airway responsiveness to hypertonic saline. The success rate of sputum induction in children is 68-100%. Most studies have processed sputum using the plug selection method, and show that the dominant cell in sputum from normal children is the macrophage, and that the upper normal limit for sputum eosinophils in children is 2.5%. The inflammatory response in childhood asthma is characterized by elevated numbers of sputum eosinophils, and eosinophil cationic protein concentration, as well as increased nitric oxide and hydrogen peroxide levels in exhaled breath. Sputum eosinophils correlate with objective markers of disease severity in steroid-naive children with asthma, and in severe asthma. Inflammatory marker levels are lower in children using glucocorticosteroids. Induced sputum and exhaled gases are important markers of inflammation in childhood asthma. The clinical utility of these markers warrants further study.