Comparison of blood gas analyser, pH meter and pH Strip methods in the measurement of pleural fluid pH

Jee, Hyun Suk; Park, Yong Bum; Choi, Jae Chol; Ahn, Chang Hyuk; Yoo, Ji Hoon; Kim, Jae Yeol; Park, In Won; Choi, Byoung Whui

Abstract

BACKGROUND
pH measurement is an important test in assessing the etiology of pleurisy and in identifying complicated parapneumonic effusion. Although the blood gas analyzer is the' gold standard method' for pleural pH measurement, pH meter & pH strip methods are also used for this purpose interchangably. However, the correlation among the pH data measured by the three different methods needs to be evaluated. In this study, we measured the pH of pleural fluid with the three different methods respectively and evaluated the correlation among the measured data.
METHODS
From August 1999 to March 2000, were measured the pleural fluid pH in 34 clinical samples with three methods-blood gas analyzer, pH meter, and pH strip. In the blood gas analyzer and pH meter methods, the temperature of plerual fluid was maintained around 0â„ƒ in air-tight condition before analysis and measurement was performed within 30 minutes after collection. As for the pH strip method, the pleural fluid pH was checked in the ward immediately after tapping and in the clinical laboratory of our hospital. This part is unclear.
RESULTS
The causes of pleural effusion were tuberculosis pleurisy in 16 cases, malignant pleural effusion 5 cases, parapneumonic effusion 9 cases, empyema 3 cases, and congestive heart failure 1 case. The pH of pleural fluid (mean±SD) was 7.34±0.12 with blood gas analyser, 7.52±0.25 with pH meter, 7.37±0.16 with pH strip of immediate measurement and 6.93±0.201 with pH strip of delayed measurement. The pH measured by delayed pH strip measurement was lower than those of other methods(p<0.05). The correlation of the results between the blood gas analyzer and pH meter(p=0.002, r=0.518) and the blood gas analyzer and pH strip of immediate measurement(p<0.001, r=0.607).
CONCLUSION
In the determination of pH of pleural fluid, pH strip method could be a simple and reliable method under immediate measurement conditions after fluid tapping.