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

ObjectiveTo determine the diagnostic utility of adenosine deaminase (ADA) in a large series of pleural effusions of different etiologies.MethodsA 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.ResultsPleural tuberculosis (TB) accounted for 221 (10.5%) effusions. Pleural fluid ADA > 35 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%).ConclusionWhere 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.