Induced sputum in children: feasibility, repeatability, and relation of findings to asthma severity

Background-The collection of induced sputum provides a non-invasive method of investigating airway inflammation. Few studies have been performed in ch ildren, so a study was undertaken to determine the feasibility of sputum in duction, the repeatability of eosinophil counts and sputum eosinophil catio nic protein (ECP) levels, and the relation of these to current asthma sever ity. For comparison, serum ECP levels were also measured. Methods-In a cross sectional study of children aged 5-15 years, 27 healthy children and 60 with asthma underwent sputum induction using inhaled nebuli sed hypertonic saline. The whole sputum sample was used for analysis. Ten c hildren with stable asthma repeated the procedure within 10 days. Results-A satisfactory sample (>500 non-squamous cells) was obtained in 61% of children with asthma and in 60% of healthy controls. The limits of agre ement within subjects ranged from a 0.68 to 2.8 fold difference for eosinop hil differential counts and from 0.38 to 4.4 fold for sputum ECP. Despite a median of 42% squamous cells, significant differences were found between a sthma and healthy controls for the eosinophil differential count (p = 0.000 4), total eosinophil counts (p = 0.03), and sputum ECP level (p = 0.0001). Overall, there was no correlation between any marker of airway inflammation and asthma severity; however expressed, including lung function. Conclusions-Sputum induction is only possible in a proportion of children. The repeatability of sputum cell counts and ECP levels, measured in a small number of children, was similar to that reported in adults. Sputum analysi s revealed no evidence of airway inflammation in a number of highly symptom atic children with asthma.