In a previous study done at our institution, we reported a statistically significant decrease in pleural fluid pH when samples were delayed up to two hours after collection. The aim of this study is to investigate the effect of WBC on pleural fluid pH values measured at various time intervals.
This is a prospective study at an academic tertiary medical center. From 40 consecutive (n=40) 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. In addition, WBC count was determined at T0 by an automated WBC counter.
With the heparinized syringes, there was a statistically significant negative correlation between pleural fluid pH and WBC at T1 and T2. With the non-heparinized syringes, there was a statistically significant negative correlation between pleural fluid pH and WBC only at T2.(table 1).
Our data showed an effect of WBC on pleural fluid pH measurement. For pleural fluid samples collected in non-heparinized syringes, there is up to two hours time before the WBC will have its effect on pH measurements. While for pleural fluid samples collected in heparinized syringes, the effect of WBC on pH measurements starts at one hour after collection of pleural fluid sample.
It is advisable to process pleural fluid for pH measurements no later than one hour of collection when using heparinized syringes, and up to two hours when using non heparinized syringes.
Table 1Type of syringe & timerpH - T00.160.32H - T10.340.03H - T20.450.003NH - T00.130.42NH - T10.260.10NH - T20.2640.001
Ali Debek, None.