What is the key question?

• Both pleural fluid pH and glucose have been suggested as accurate markers for determining the character of a pleural effusion. It is unknown whether levels of one may predict the other.

What is the bottom line?

• This trial aimed to investigate any potential correlation between pH and glucose in pleural fluid and whether further information could be gained by testing both when compared to testing each individually.
• pH and glucose measurements were obtained from 2971 samples. They were characterised by groups into cancer, infection, tuberculosis or others. The correlation between pH and glucose where assessed using clinically relevant cut-offs (pH 7.2 and glucose 3.3mmol/L).
• Mean pH was 7.38 and median glucose 5.99mmol/L. The relationship between pH and glucose was concordant in 91.9% of samples using the above cut-offs. pH alone detected 95% of infection related effusions and glucose alone detected 91.7% when either value was below the cut-off.

Why read on?

• This study suggests performing either assay provides the same information greater than 90% of the time. This may help reduce concern in relation to sample deterioration when specimens for pH are collected but measurement is delayed.