ADA1/ADAp ratio in pleural tuberculosis: an excellent diagnostic parameter in pleural fluid

We analysed the efficacy of pleural adenosine deaminase (ADAp) and the ADA1/ADAp ratio in the diagnosis of pleural tuberculosis in 103 pleural effusions, 27 of which were tuberculosis (TB) and 76 other diagnoses (non-TB). Smears, cultures and pleural biopsies were carried out in all cases, and were used for final diagnosis. The diagnostic yield of the parameters under study were as follows: smears/cultures of mycobacteria in fluid 11.1%/33.3%; biopsy 33.3%/51.8% and tuberculosis granulomas 85.1%. The levels of ADAp and ADA1/ADAp ratio in TB and non-TB groups showed very significant differences (P < 0.00001); in the TB group: ADAp 54.7 +/- 23.5 IU and ADA1/ADAp 0.27 +/- 0.08; in the non-TB group: ADAp 18.3 +/- 43.2 IU and ADA1/ADAp 0.64 +/- 0.14. The assay established ADA levels in pleural fluid > or = 40 IU and an ADA1/ADAp ratio < or = 0.42 as cut-off levels to identify individuals in the TB group, with a sensitivity of 88.8%/100%, a specificity of 92%/98.6%, a positive predictive value (PPV) of 80%/96.4%, a negative predictive value (NPV) of 95.8%/100% and an accuracy of 91.2%/99.02%. The ADAp levels in 27 patients with TB, showed close correlation with the number of monocyte macrophages (P = 0.001), but not with the number of lymphocytes (P = n.s.). The ADA1/ADAp ratio overcomes the limitations of ADAp (false positives and negatives), and is the most useful parameter for diagnosis on account of a high diagnostic yield, low cost and speed of the assay for identifying a pleural tuberculosis diagnosis, when compared with traditional methods.