title: Exhaled breath condensate pH and childhood asthma: unselected birth cohort study.
abstract: BACKGROUND
  Exhaled breath condensate pH (EBC-pH) may be useful noninvasive marker for evaluation of patients with asthma.
  
  
  OBJECTIVE
  To investigate the relationship between EBC-pH and symptoms suggestive of childhood asthma in an epidemiologic setting and examine its relation to lung function, airway hyperresponsiveness (AHR), and airway inflammation.
  
  
  METHODS
  Within the context of a prospective population-based birth cohort, EBC was collected from 630 children at age 8 yr using the RTube (pH measured after deaeration with argon). Lung function was measured by spirometry (FEV1; n = 521) and plethysmography (sRaw; n = 567), and AHR by methacholine challenge (n = 498). Airway inflammation was assessed using exhaled nitric oxide (eNO; n = 305).
  
  
  RESULTS
  EBC-pH values ranged widely (4.40-8.29), and did not differ between 54 children with parentally reported asthma and 562 nonasthmatic subjects (median [interquartile range]: 7.75 [7.45-7.85] vs. 7.77 [7.59-7.87]; p = 0.35). There was a trend for lower EBC-pH among current wheezers (n = 98; 7.72 [7.50-7.83]) compared with nonwheezers (n = 532; 7.77 [7.60-7.87]; p = 0.07). Wheeze frequency, severity, and use of antiasthma medication were not associated with EBC-pH. There was no consistent association between EBC-pH and lung function, airway reactivity, and airway inflammation (FEV1, sRaw, PD20 methacholine, or eNO). There was no significant difference in EBC-pH between current wheezers receiving asthma medication who had positive methacholine challenge compared with children without any of these features.
  
  
  CONCLUSIONS
  In the epidemiologic setting, EBC-pH does not differ between children with and without parentally reported symptoms suggestive of asthma. We found no consistent association between EBC-pH and lung function, AHR, and airway inflammation in this sample from the general population.
authors: University of Manchester; and North West Lung Centre, Wythenshawe Hospital, Manchester, United Kingdom. nicolaos.nicolaou@postgrad.manchester.ac.uk
authors: Nicolaos C
authors: NC
authors: Nicolaou
authors: Lesley A
authors: LA
authors: Lowe
authors: Clare S
authors: CS
authors: Murray
authors: Ashley
authors: A
authors: Woodcock
authors: Angela
authors: A
authors: Simpson
authors: Adnan
authors: A
authors: Custovic