Comparison of the use and accuracy of methods for determining pleural fluid pH

Background. The blood gas analyzer (BGA) has been considered the "gold standard" for pleural fluid pH determination. Methods. We report the various methods used to measure pleural fluid pH by 277 acute care institutions who responded to a mailed questionnaire. The techniques used included the BGA (32%), dip stick or pH indicator paper (56%), and a pH meter (12%). We tested 36 consecutive exudative pleural fluid samples using each method. Results, The alternative methods were incomparable to accurately measuring pleural fluid pH by the BGA, with a mean difference of 0.16 pH unit. With a delay in testing, the pH of the pleural fluid was more alkalotic and variable, with a mean difference of 0.039 pH unit. Conclusions. Clinicians should be encouraged to test selected samples for pleural fluid pH by the BGA when accurate measurements will influence therapy.