Combination of adenosine deaminase activity and polymerase chain reaction in bronchoalveolar lavage fluid in the diagnosis of smear-negative active pulmonary tuberculosis

Abstract

Some studies have assessed the diagnostic value of adenosine deaminase (ADA) activity in bronchoalveolar lavage fluid (BALF) in the diagnosis of pulmonary tuberculosis (TB). However, a conclusion has not been reached due to the limited number of patients with various pulmonary diseases used as comparators. The objective of this study was to evaluate the efficacy of BALF ADA activity and TB PCR assay for diagnosing pulmonary TB. BAL samples from 424 patients with acid-fast bacillus-negative sputum smears who underwent bronchoscopy for diagnostic evaluations of pulmonary diseases, were prospectively analyzed for ADA activity and TB PCR. The median ADA activity of TB cases was significantly different from that of patients with solid tumor without endobronchial obstruction (p<0.001), inactive TB (p=0.04), and other (p=0.038), while this was not the case for the other pulmonary diseases. A cutoff BALF ADA activity of ≥3 U/l provided a sensitivity of 58.7% and specificity of 81.8% to differentiate TB from solid tumor without endobronchial obstruction. The sensitivity of TB PCR in BALF was 28.1% with a specificity of 99.0%. The area under the receiver operating characteristic (ROC) curve to differentiate TB from solid tumor without endobronchial obstruction was significantly higher for the combination of ADA activity ≥3 U/l and TB PCR (0.77) than for ADA activity ≥3 U/l alone (0.70, p<0.001) or for TB PCR alone (0.64, p<0.001). The sensitivity of the combination of ADA activity ≥3 U/l and TB PCR was 72.7% and the specificity was 81.8%. In TB cases, a greater radiographic extent of disease was associated with a higher median ADA activity (p=0.017). BALF ADA had limited value in differentiating pulmonary TB from some other pulmonary diseases. To differentiate TB from solid tumor without endobronchial obstruction, a combination of BALF ADA and TB PCR had marked additive diagnostic value.