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Normative Data for pH of Exhaled Breath Condensate: Statistical Analysis

Normative Data for pH of Exhaled Breath Condensate: Statistical AnalysisData are reported as median and interquartile range (25 to 75%), as well as 5 to 95% ranges and full ranges. For comparisons between sexes and among age ranges and races, analysis was performed by rank-sum testing or analysis of variance on ranks with appropriate pair-wise comparisons using software (Sigmastat 3.0; Systat Software; Point Richmond, CA).
Four hundred twelve subjects were enrolled and provided a single EBC sample for this study. The subject population is described in Table 2. Of the 412 subjects enrolled, 404 provided sample volumes sufficient for EBC pH assay, a success rate > 98%, The median EBC pH of this healthy population was 8.0 with interquartile (25 to 75%) range of 7.8 to 8.1 (Fig 1). The maximum EBC pH was 8.4, and the minimum pH was 4.5. The values were the same for female patients (median, 8.0; interquartile range, 7.8 to 8.1; n = 248) and male patients (median, 8.0; interquartile range, 7.9 to 8.1; n = 154; p = 0.31) [Fig 2]. EBC pH values for 10-year age brackets were determined (Table 2; Fig 3), and again these medians were 8.0 to 8.1 with no differences identified by analysis of variance on ranks (p = 0.27). EBC pH < 7.3 accounted for 6.4% of the samples. canadian health&care mall

In this study, we have demonstrated that in healthy subjects, the median, gas-standardized EBC pH is 8.0 with an interquartile range of 7.8 to 8.1. The data are tightly clustered in a mildly nonpara-metric bell curve. This normal range provides additional context to the published data revealing prominently lower values in patients with multiple respiratory disease states (with EBC pH often in the pH 4 to 6 range). Our data present a range that is slightly higher than that from previously published control subjects, which in part reflects that means ± SD are more commonly reported and the mean is brought down by control outliers. The mean pH of this current data set is 7.85, consistent with previous data (although this data set is not parametric). Some prior studies may have performed the gas standardization less completely than is currently done.

Table 2—EBC pH by Decade of Life

Age Group, yr/ No. of Subjects EBC pH, Mean ± SD EBC pH Median EBC pH 25 to 75% Interquartile Range EBC pH 5 to 95% Intervals
0-10/12 8 ± 0.3 8.1 8.0-8.1 7.6-8.3
11-20/163 7.8 ± 0.7 8.0 7.8-8.1 6.5-8.3
21-30/122 7.8 ± 0.6 8.0 7.8-8.1 6.8-8.2
31-40/24 8.0 ± 0.2 8.1 8.0-8.1 7.5-8.2
41-50/30 7.9 ± 0.6 8.0 7.9-8.1 7.3-8.3
51-60/27 7.9 ± 0.5 8.0 7.9-8.1 7.4-8.2
61-70/17 8.0 ± 0.2 8.0 7.9-8.1 7.7-8.1
> 71/6 8.0 ± 0.2 8.1 7.9-8.2 7.7-8.2

Figure-1

Figure 1. Distribution of EBC pH values in 404 healthy subjects. Median EBC pH is 8.0 (interquartile range, 7.8 to 8.1). Samples were collected for 7 min using a disposable commercially available polypropylene collector at temperatures that ensured condensation in liquid phase as opposed to as ice crystals.

Figure-2

Figure 2. EBC pH values for healthy female and male subjects.

Figure-3

Figure 3. EBC pH values separated based on decade of life.

This entry was posted in Pulmonary function and tagged airway pH, exhaled breath condensate, reference ranges.
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