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.