Urinary eosinophil protein X in children with asthma: influence of atopy and airway infections.

It has been suggested that urinary eosinophil protein X (U-EPX) can be used to monitor bronchial inflammation in childhood asthma. However, the influence of atopy and airway infections is not well elucidated. To determine the clinical value of measuring U-EPX in children with asthma and to evaluate the influence of atopy and airway infections, U-EPX was measured in 170 children with asthma (mean age 69 months, range 12-179 months), in 79 children with lower or upper respiratory tract infections (mean age 41 months, range 1-165 months), and in 64 controls. U-EPX was elevated in children with acute asthma (median 132 microg/mmol of creatinine, quartiles 77-195 microg/mmol of creatinine, n = 51, p <0.001) and chronic asthma (median 93 microg/mmol of creatinine; quartiles 46-149 microg/mmol of creatinine, n = 119, p <0.01) compared with controls (median 54 microg/mmol of creatinine, quartiles 40-89 microg/mmol of creatinine, n = 39). Atopic children had higher levels of U-EPX than non-atopics with acute asthma (median 155 microg/mmol of creatinine, quartiles 113-253 microg/mmol of creatinine, n = 27, vs. median 102 microg/mmol of creatinine, quartiles 56-168 microg/mmol of creatinine, n = 24, p <0.05), as well as with chronic asthma (median 110 microg/mmol of creatinine, quartiles 65-162 microg/mmol of creatinine, n = 63, vs. median 60 microg/mmol of creatinine, quartiles 39-123 microg/mmol of creatinine, n = 56, p <0.01). In chronic asthma, children without atopy had levels of U-EPX similar to values of controls; levels were similar in symptomatic and asymptomatic patients, and not influenced by treatment with inhaled corticosteroids. Moreover, U-EPX levels were higher in children with pneumonia (median 207 microg/mmol of creatinine, quartiles 111-280 microg/mmol of creatinine, n = 35, p <0.001), laryngitis (median 109 microg/mmol of creatinine, quartiles 65-161 microg/mmol of creatinine, n = 24, p <0.01), and rhinitis (median 172 microg/mmol of creatinine, quartiles 123-254 microg/mmol of creatinine, n = 19, p <0.001) than in controls (median 62 microg/mmol of creatinine, quartiles 41-93 microg/mmol of creatinine, n = 64). There was significant overlap among all groups of children with disease, as well as between children with disease and controls. Hence, U-EPX may reflect differences in eosinophil involvement and activation between children with atopic and non-atopic asthma, but the individual spread within groups and the influence of airway infections limits the clinical value of U-EPX in childhood asthma.