Seasonal differences of peak expiratory flow rate variability and mediators of allergic inflammation in non‐atopic adolescents

Variations in peak expiratory flow (PEF) and serum eosinophil mediators were studied in healthy adolescents. Twenty-five boys and 31 girls, 11-16 years of age (mean age 14.3 years), were selected and investigated during the birch pollen season of 1995; 45 were also investigated during the autumn of the same year. The PEF was measured twice daily and eosinophil mediators in serum and in urine were measured by radioimmunoassay (RIA) once during the birch pollen season and once in autumn. The type values of the daily PEF variation, expressed in amplitude percentage mean, were 6.4 and 3.9%, mean values were 7.35 and 6.74%, and the 95th percentiles were 18 and 14%, during the birch pollen season and autumn, respectively. The 95th percentiles were 41 and 38 microg/l for serum eosinophil cationic protein (s-ECP), 74 and 62 microg/l for serum eosinophil protein X (s-EPX), 987 and 569 microg/l for serum myeloperoxidase (s-MPO), and 165 and 104 microg/mmol for urinary eosinophil protein X/urinary creatinine (u-EPX/u-creatinine), during the birch pollen season and autumn, respectively. The levels of the eosinophil mediators decreased significantly from May (n = 56) to November (n = 45), for s-ECP from a median value of 14 microg/l to 7 microg/l (p= 0.001), for s-EPX from a median value of 28 microg/l to 20 microg/l (p= 0.001), and for the neutrophil mediator, s-MPO, from a median value of 440 g/l to 292 g/l (p< 0.001). The PEF variability decreased significantly (p= 0.037), from spring (n = 55; median 8%, 95% confidence interval [CI] 7.8-10.19) to autumn (n = 44; median 6%, 95% CI 6.1-8.9). A significant correlation was found between the levels of s-ECP and s-EPX (rs = 0.7, p< 0.001), between s-ECP and s-MPO (rs = 0.6, p< 0.001), between s-EPX and s-MPO (rs = 0.4, p< 0.005), and between s-EPX and u-EPX/u-creatinine (rs = 0.6, p< 0.0001), in the birch pollen season (n = 56) and in the autumn (n = 45). There was a positive correlation found in PEF variability between the two seasons (n = 43; rs = 0.5, p= 0.0006). No other correlation was found between PEF variability and any other parameters. The difference in the levels of eosinophil mediators between seasons in non-atopic, healthy children is unexplained. Normal limits for mediators were higher and PEF variability was almost the same as has been reported in adults. When using normal values, seasonal influences should be considered.