Comparison of the Accuracy of Different Methods for Determining Pleural Fluid pH

Document Type

Review

Publication Date

10-1-1998

Description

Purpose: An accurate pleural fluid (PF) pH is helpful in the management of malignant and parapneumonic pleural effusions. The blood gas analyzer (BGA) has been considered the "gold standard" for PF pH determination. Manufacturers of BGA do not recommend testing fluids other than blood on their machines. Laboratories, therefore, are under increasing pressure to find alternative means to measure PF pH. We undertook this study to determine if alternative methods of PF pH measurement are comparable. Methods: Thirty-six consecutive patients undergoing diagnostic thoracentesis during the day were enrolled. Transudative and grossly purulent effusions were excluded from the study. PF pH was immediately measured by BGA, pH indicator paper, urine dip stick, and pH meter. pH determination by each method was performed by a single individual dedicated to one method and blinded to the authors. Results: Twenty-five patients had exudative, non-purulent pleural effusions. When compared to the BGA the mean pH was significantly different for each alternative method. The mean of the differences for each alternative method of PF pH determination was greater than 0.16 units. The pH meter was the least reliable method at our institution. Conclusions: pH indicator paper, dip stick, and pH meter are not dependable options to ascertain an correct pH of PF at our institution. Inaccurate determinations may result in inappropriate management decisions. Until further data are available and a reliable alternative method of determining PF pH is validated, we suggest that the BGA remain the method of choice to measure PF pH.

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