Adenosine Deaminase Activity in Tuberculous and Malignant Pleural Effusions

Measurement of pleural adenosine deaminase activity (ADA) is a useful diagnostic tool for tuberculous pleurisy, but false-positive findings from non-tuberculous effusions have been reported. In order to improve diagnostic value of ADA it is recommended to estimate activity of both ADA1 and ADA2 izoenzymes or 2′-deoxyadenosine/adenosine activity ratio. In order to evaluate ADA as a diagnostic parameter total ADA, with adenosine as a substrate, and 2’-deoxyadenosine/adenosine activity ratio were measured in tuberculous and malignant pleural effusions. Altogether, 26 pleural exudates (11 tuberculous and 15 malignant) were selected. ADA either with adenosine or 2’-deoxyadenosine was determined by colorimetric method of Giusti. Each pleural fluid sample was diluted prior to the assay (1:8) to avoid enzyme inhibition which was observed in nondiluted pleural effusions. The ADA level reached the diagnostic cut-off set for tuberculous effusions (40 U/L) in every 11 tuberculous exudates with the mean value of 85.3 ± 47.1 U/L; in 9 of these the 2′-deoxyadenosine/adenosine ratio was less than 0.45. In the malignant group of patients, no one ADA level exceed 40 U/L, being estimated at 10.6 ± 7.7 U/L (p < 0.001). In 10 of these 15 exudates the 2′-deoxyadenosine/adenosine ratio was undetectable, in four it was less than 0.45 and only in one it was over 0.45.We concluded that ADA measured by the Giusti method proceeded by the dilution 1:8 of the pleural effusion samples very good differentiates tuberculous from malignant pleurisy, without the necessity to determine the 2′-deoxyadenosine/adenosine ratio The investigation needs to be continued on the more numerous groups of patients.