Diagnosis of extrapulmonary tuberculosis by Gen-Probe amplified Mycobacterium tuberculosis direct test

A total of 294 specimens collected from nonrespiratory sites of 268 patients were tested for direct detection of Mycobacterium tuberculosis complex by the Gen-Probe Amplified Mycobacterium tuberculosis Direct Test (AMTD). The specimens included ascitic, pleural, pericardial, and synovial fluids, abscess aspirates, and tissue and lymph node biopsy samples, as well as gastric aspirates and cerebrospinal fluid samples. All samples were processed by the N-acetyl-L-cysteine-sodium hydroxide decontamination procedure prior to testing. Twenty samples showed acid-fast bacilli on auramine staining, and 48 samples were positive by AMTD, 9 of which were negative for M. tuberculosis complex by culture. After reviewing the patients clinical charts to resolve discrepancies, the test result of one cerebrospinal fluid sample was considered to be false positive by AMTD. The overall sensitivity, specificity, positive predictive value, and negative predictive value were 83.9, 99.6, 97.9, and 96.3%, respectively. No significant differences were found when AMTD results obtained with specimens of nonrespiratory origin were compared with assay results obtained with samples of respiratory origin (P > 0.05). In conclusion, our results demonstrate that AMTD performs equally well with all types of specimens.