Pleural fluid pH measurement is an important tool for characterizing the type of pleural fluid, establishing a diagnosis, and guiding clinical management. The current standard and widely accepted practice is to collect pleural fluid samples for pH measurement in heparinized syringes and to instantaneously process these samples at room temperature. We conducted a prospective study to investigate the changes in pleural fluid pH measurements collected in heparinized versus non heparinized syringes and processed at various time intervals while the samples are preserved at room temperatur.
This is a prospective study in an academic tertiary medical center. From 50 consecutive (n=50) thoracentesis, 1ml of pleural fluid was collected anaerobically in each of six 3 ml syringes. Three syringes were coated with heparin. Samples in each syringe type (heparinized (H) and non-heparinized (NH)) were processed for pleural fluid pH measurements at time 0 (T0), one hour (T1) and two hours (T2) post collection. All specimens were preserved at room temperature until the measurements were carried out in duplicates by a calibrated blood gas analyzer.
Pleural fluid pH values were significantly (p<0.05) lower when collected in heparinized versus non-heparinized syringes at all time intervals (T0: pH(H)=7.37±0.10 vs. pH(NH)=7.39±0.10, T1: pH(H)=7.37±0.11 vs. pH(NH)= 7.39±0.11, T2: pH(H)=7.37±0.12 vs. pH(NH)=7.38±0.11). With heparinized syringes, there was a significant (p<0.05) decrease in pleural pH values only at T2 versus T1. There were no significant changes in pleural pH values over time with the non-heparinized syringes.
There were statistical differences in the values of pleural pH when using heparinized versus non-heparinized syringes.In heparinized syringes, the pleural pH values decreased at two hours but not at one hour post collection, therefore it is advisable to process pleural fluid for pH measurements no later than one hour of collection when using heparinized syringes.
for serial pleural pH measurements the same type of syringes (either heparinized or non-heparinized) should be consistently used and samples collected in heparinized syringes can be processed up till one hour of collection.
Ali Debek, None.