title: Methacholine challenge test results in children are season dependent.
abstract: BACKGROUND
  It is known that several parameters influence the positivity of a methacholine challenge (MCH), including a recent viral disease, allergies, and air pollution. Reports regarding the influence of the season upon the positivity of MCH are scarce. The aim of this study was to assess the percentage of positive MCH tests per season.
  
  
  METHODS
  We retrospectively evaluated all MCH tests performed in children and adults in a single center over a 30-month period. The percentage of positive tests for summer was compared with that of other seasons.
  
  
  RESULTS
  A total of 155 challenges were performed in children (under 20 years old) and 527 in adults. Thirty-eight percent of the tests were positive in adults and 71 % in children. The percentage of positive tests in the summer was significantly lower than the percentage of positive results during the rest of the year in children (58.5 vs. 75.4 %, respectively; p = 0.046). By contrast, there was no difference between the seasons in adults (39 vs. 38 %, respectively; p = 0.92).
  
  
  CONCLUSIONS
  There is a difference of 22.4 % in the percentage of positive tests in the summer months compared to the rest of the year in children, suggesting a reduction in the sensitivity of the MCH test in the hot season. We suggest that in cases where asthma is strongly suspected in a child and the MCH test was negative in the summer, one should consider repeating the MCH test in another season.
authors.affiliation: Pediatric Pulmonary Unit, Department of Pediatric Pulmonology, Shaare Zedek Medical Center, Affiliated with the Hebrew University School of Medicine, P.O. Box 3235, 91031, Jerusalem, Israel, leonj@doctors.org.uk.
authors.forename: Leon
authors.initials: L
authors.lastname: Joseph
authors.forename: Elie
authors.initials: E
authors.lastname: Picard
authors.forename: Bosmat
authors.initials: B
authors.lastname: Dayan
authors.forename: Shmuel
authors.initials: S
authors.lastname: Goldberg
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001249:Asthma / Q000139:chemically induced / Q000175:diagnosis / Q000453:epidemiology*; D001985:Bronchial Provocation Tests; D002648:Child; D002675:Child, Preschool; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D015994:Incidence; D008297:Male; D016210:Methacholine Chloride / Q000009:adverse effects*; D008875:Middle Aged; D012130:Respiratory Hypersensitivity / Q000139:chemically induced / Q000175:diagnosis / Q000453:epidemiology*; D012189:Retrospective Studies; D012621:Seasons; D055815:Young Adult
chemical_list: D016210:Methacholine Chloride