Prospective longitudinal study of urinary eosinophil protein X in children with asthma and chronic cough

Airway inflammation is the principal abnormality in asthma and many other respiratory diseases. Eosinophils are the cells primarily involved in this process. The aim of this study was to analyze sequential changes in urinary eosinophil protein X (EPX) a biological marker of eosinophil activation in asthmatic children and chronic coughers, and to confirm the importance of such changes in evaluating the inflammatory process once regular treatment was initiated. Eighty-eight asthmatic children (AC), 33 children with chronic cough (CC), and 34 control children were included in the study. All those with respiratory disease underwent allergy tests (serum total IgE, serum-specific IgE for common allergens, peripheral blood eosinophil (PBE), and skin prick tests) and a pulmonary function test (PFT), and had chest X-ray and serum eosinophil cationic protein (s-ECP) and urinary EPX assays. All subjects attended the outpatient clinic every 3 months, irrespective of the treatment prescribed following inclusion in this investigation. At baseline, urinary EPX concentrations were higher in children with asthma and those with chronic cough than in controls (mean 171.1 and 131.3, respectively, vs. 60.2 microg/mmol creatinine, P < 0.001). CC children had lower eosinophil counts (0.25 vs. 0.39 x 10(9)/L, P < 0.02) than those with asthma. There was no significant difference between the AC and CC groups in urinary EPX and s-ECP levels. s-ECP concentrations were significantly higher (P < 0.01) in atopic vs. nonatopic patients (44 vs. 29.9 ng/mL), but no significant difference was observed for urinary EPX. Concentrations of urinary EPX were significantly correlated with s-ECP levels (r = 0.24, P < 0.025) and with PBE (r = 0.38, P < 0.01). No correlation was found between urinary EPX values and PFT results. In AC receiving inhaled steroids after the start of the study, there was a significant reduction after 3 months in urinary EPX (-54, P < 0.02). In contrast, there was no significant change in PBE levels. Urinary EPX concentrations are sensitive, noninvasive technique that could be useful to the clinician in the evaluation of manifestations of airway inflammation.