Exhaled breath condensate pH and childhood asthma: unselected birth cohort study.

Rationale: Exhaled breath condensate pH (EBC-pH) may be useful noninvasive marker for evaluation of patients with asthma.

Objectives: 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.