Normative data for pH of exhaled breath condensate

Division of Neonatology, Department of Pediatrics, University of Virginia, Charlottesville, VA 22908, USA.
Chest (Impact Factor: 7.48). 03/2006; 129(2):426-30. DOI: 10.1378/chest.129.2.426
Source: PubMed


Measurement of pH is one of the simplest and most technically validated biomarkers studied in exhaled breath condensate (EBC). The pH of EBC has been found to be lower than controls in many respiratory disorders. Published data from normal control subjects have been reasonably consistent, but the data sets are not large. This study was undertaken to establish normative EBC pH reference values.
Four hundred four healthy subjects of all ages were enrolled.
Each participant provided a single EBC sample using a disposable collector at modest temperature so that EBC was collected as a liquid.
Samples of EBC were bubbled with argon gas to standardize for carbon dioxide, and pH was recorded with a calibrated and validated glass microelectrode on stabilization. The median EBC pH was 8.0 with interquartile (25 to 75%) range of 7.8 to 8.1. There were no differences based on age, sex, or race. The distribution is skewed, with 6.4% of EBC samples having a pH range < 7.4.
An extensive normal data set now exists that reveals EBC pH is maintained in a modestly alkaline and tight range in subjects who consider themselves healthy.

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    • "Acidification occurs in several respiratory diseases (Borrill et al., 2008; Hunt, 2007; Horvarth et al., 2005). The level of EBC pH is unaffected by variables that include subject age, race, gender, collecting and storage temperature, acute airway obstruction, ammonia in the mouth, saliva pH, hyperand hypoventilation (Bloemen et al., 2007; Paget-Brown et al., 2006; Borrill et al., 2005; Wells et al., 2005; Vaughan et al., 2003). Acidification of EBC occurs in acidic materials generated from inflammatory cells (Hunt et al., 2002), and gastroesophageal reflux (Effros et al., 2005). "
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    • "The methods used in this study for pH measurement have been validated and were previously shown to be robust and reliable [9,13,24]. Normative data were characterized in 404 healthy subjects [26]. Our findings of EBC pH values measured immediately after collection or with deaeration corroborate our previous results and are in accordance to the published data referring to ECoScreen [6,15]. "
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    • "Another possibility is that low pH values representing endogenous intermittent airway acidification events are normal rather than pathologic phenomena. Supporting this speculation are several recent studies that measured breath pH among healthy controls (Table 3) and found surprisingly low breath pH in a subset of subjects [25,29], including one large population-based study that found breath pH values as low as 4.4 in healthy children [30]. The possibility that intermittent low breath pH values reflect normal biologic processes calls into question the utility of breath pH measurement – especially one-time breath pH measurement – as a reliable biomarker of lung inflammation or respiratory health effects. "
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