Diagnostic performance of adenosine deaminase activity in pleural fluid: A single-center experience with over 2100 consecutive patients

Objective: To determine the diagnostic utility of adenosine deaminase (ADA) in a large series of pleural effusions of different etiologies. Methods: A retrospective study of 2104 consecutive patients presenting with pleural effusion was carried out at a Spanish university hospital. ADA levels in pleural fluid were determined using a non-Giusti automatic kinetic assay, and a receiver operating characteristics curve analysis was applied to estimate their discriminative properties. Results: Pleural tuberculosis (TB) accounted for 221 (10.5%) effusions. Pleural fluid ADA > N35 U/L yielded 93% sensitivity, 90% specificity, a positive likelihood ratio (LR) of 10.05 and a negative LR of 0.07 for the diagnosis of TB among lymphocytic exudates. The ADA activity was significantly higher in neutrophil-(111.6 U/L) than in lymphocyte-rich (62.4 U/L; p = 0.002) TB effusions. Overall, more than 40% of parapneumonics and half of lymphomatous effusions exceeded the cutoff set for TB. These were the only causes of ADA activity above 250 U/L. When the prevalence of TB as a cause of exudative effusions is low (e. g., 1%), the estimated positive predictive value of the ADA test may be as low as 7%, although the negative predictive value remains high (99.9%). Conclusion: Where available, pleural ADA should be routinely used to rule TB in or out in areas with moderate to high or low TB prevalence, respectively. A high ADA level is a characteristic not only of lymphocytic, but also of neutrophilic TB effusions. An extremely high ADA activity should raise suspicion of empyema or lymphoma. (C) 2010 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved.