Comparison of pleural fluid pH measurements: blood gas analyzer, pH indicator stick, litmus paper, and point-of-care testing for blood gases

Abstract

The measurement of pleural fluid pH helps to determine the causes of the effusion. The accuracy of blood gas analyzers (BGA) in the measurement of pleural fluid pH was well known. However, many of the laboratories continue to use inaccurate methods such as pH indicator stick and litmus paper. The purpose of the present study was to compare the pleural fluid pH values determined by BGA, pH indicator stick, litmus paper, and point-of-care testing for blood gases (POCT-BG). The pleural fluid pH was measured by four methods within 20 minutes after being collected and then followed routine laboratory procedures in pleural fluids from 42 patients, prospectively. We calculated the intraclass correlation coefficient (ICC) to figure out an absolute agreement among the values from the different methods. A high ICC close to 1.0 indicates high similarity between values. The mean pleural pH was 7.61±0.14 (BGA), 7.58±0.23 (indicator stick), 7.32±0.21 (litmus paper), and 7.42±0.14 (POCT-BG), respectively. The ICC value was the highest of 0.84 between the values from BGA and POCT-BG. The ICC values were calculated of 0.40 (BGA and indicator stick) and 0.15 (BGA and litmus paper), respectively. In conclusion, analytical performance of POCT-BG was comparable to BGA. When the pleural pH is going to be needed for decision making, we can also use POCT-BG which has the advantage of easiness, instead of using BGA.