Measuring pleural fluid pH - High correlation of a handheld unit to a traditional tabletop blood gas analyzer

Study purposes: To survey hospital laboratories in the United States to det ermine methods used for measuring pleural fluid pH, and to compare pleural fluid pH values obtained with a traditional tabletop blood gas analyzer (BG A) to those obtained with a handheld analyzer. Methods: Hospital laboratories nationwide were contacted by telephone to su rvey the methods used to measure pleural fluid pH. In a second phase, pleur al fluid was prospectively collected from 19 pediatric and adult patients w ith pleural effusions, and pleural fluid pH was measured simultaneously wit h a traditional tabletop BGA and with a handheld unit. Results: A total of 220 hospital laboratories were contacted by telephone, and 166 responded (75%). The methods for determining pleural fluid pH for a ll hospital laboratories were pH meter (35%; n = 59), BGA (32%; n = 53), an d litmus paper (31%: n = 51); 2% (n = 3) did not perform the test. Universi ty hospitals were more likely to use a BGA, compared to community hospitals (p < 0.014) or children's hospitals (p < 0.001). In the comparison of pleu ral fluid measurements, the mean pH for the traditional BGA was 7.358 +/- 0 .189, and the mean pH for the handheld unit was 7.382 +/- 0.203. The absolu te difference between the two machines was 0.024 U, and the two methods wer e correlated (p < 0.01; r = 0.993; degrees of freedom = 36). Conclusion: Most hospital laboratories in the United States do not measure pleural fluid pH using a traditional BGA and use alternative methods that h ave previously been shown to be inaccurate. Pleural fluid pH obtained by a handheld unit has a high degree of correlation to that of a traditional tab letop BGA, and it offers a satisfactory alternative for laboratories reluct ant to measure pleural fluid pH with a BGA.