title: Relationship between airway neutrophilia and ageing in asthmatics and non-asthmatics.
abstract: OBJECTIVE
  Increased sputum neutrophilia has been observed in asthma, but also during normal ageing in asthmatics and non-asthmatics. It remains unclear what constitutes 'normal' neutrophil levels in different age groups.
  
  
  METHODS
  We assessed the relationship between age and airway neutrophils of 194 asthmatics and 243 non-asthmatics (age range: 6-80 years). Regression analyses were used to assess this relationship adjusted for confounders including asthma status, atopy, gender, smoking and current use of inhaled corticosteroids (ICS). Age-corrected reference values for different age groups were determined using the 95th percentile of non-asthmatic participants.
  
  
  RESULTS
  Age was positively associated with sputum neutrophils in both asthmatic and non-asthmatic adults (0.46% neutrophil increase/year (95% confidence interval (CI) 0.18, 0.73) and 0.44%/year (0.25, 0.64, respectively), but no association was found in the <20-year age category. Individuals with high sputum neutrophil counts (>95th percentile of non-asthmatic counts for any given age group) were significantly more likely to be asthmatic (odds ratio = 2.5; 95% CI: 1.3, 5.0), with the greatest effect observed in the older age group. Other factors that independently associated with increased sputum neutrophil levels included atopy in non-asthmatic adults, male gender and current use of ICS in asthmatic adults. Age-specific reference values for neutrophil percentage were under 20 years-76%, 20-40 years-62%, 40-60 years-63% and over 60 years-67%.
  
  
  CONCLUSIONS
  Airway neutrophilia is related to age in adults, with a neutrophilic asthma phenotype present in older adults. The use of appropriate age-specific reference values is recommended for future studies aimed at elucidating the role of neutrophils in asthma.
authors.affiliation: Centre for Public Health Research, Massey University Wellington Campus, Wellington, New Zealand. c.r.brooks@massey.ac.nz
authors.forename: Collin R
authors.initials: CR
authors.lastname: Brooks
authors.forename: Peter G
authors.initials: PG
authors.lastname: Gibson
authors.forename: Jeroen
authors.initials: J
authors.lastname: Douwes
authors.forename: Christine J
authors.initials: CJ
authors.lastname: Van Dalen
authors.forename: Jodie L
authors.initials: JL
authors.lastname: Simpson
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology*; D001249:Asthma / Q000473:pathology*; D002452:Cell Count; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009504:Neutrophils / Q000473:pathology*; D010641:Phenotype; D012044:Regression Analysis; D012189:Retrospective Studies; D012737:Sex Factors; D013183:Sputum / Q000166:cytology*; D055815:Young Adult