Investigation of the patient with pleural effusion.

摘要

Editor - Rahman and Munawar's paper on investigating the patient with pleural effusion (Clin Med April 2009 pp 174-8) made no mention of the utility of quantifying pleural fluid adenosine deaminase (ADA) as a diagnostic parameter. Assay of ADA is simple and inexpensive, coupled with a relatively high sensitivity and specificity in identifying tuberculous pleuritis, enhanced further when the effusion in question is richly lymphocytic. While the positive predictive value of ADA may be lowered by its use in areas of low tuberculosis (TB) prevalence, its negative predictive value should remain unaffected, retaining its overall value as a subsidiary 'rule out' test for suspected TB pleural disease. Furthermore, ADA levels falling below the diagnostic cut-off threshold (around 40 U/l) have been shown to virtually exclude TB as a cause of pleural effusion even when the collection is lymphocytic. We suspect that many physicians continue to find the analysis of ADA useful in the setting of suspected TB pleural sepsis while eagerly awaiting the emergence of newer immune-based tests of pleural fluid.