The ligase chain reaction as a primary screening tool for the detection of culture positive tuberculosis

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Abstract
BACKGROUND The ligase chain reaction Mycobacterium tuberculosis assay uses ligase chain reaction technology to detect tuberculous DNA sequences in clinical specimens. A study was undertaken to determine its sensitivity and specificity as a primary screening tool for the detection of culture positive tuberculosis. METHODS The study was conducted on 2420 clinical specimens (sputum, bronchoalveolar lavage fluid, pleural fluid, urine) submitted for primary screening forMycobacterium tuberculosis to a regional medical microbiology laboratory. Specimens were tested in parallel with smear, ligase chain reaction, and culture. RESULTS Thirty nine patients had specimens testing positive by the ligase chain reaction assay. Thirty two patients had newly diagnosed tuberculosis, one had a tuberculosis relapse, three had tuberculosis (on antituberculous therapy when tested), and three had healed tuberculosis. In the newly diagnosed group specimens were smear positive in 21 cases (66%), ligase chain reaction positive in 30 cases (94%), and culture positive in 32 cases (100%). Using a positive culture to diagnose active tuberculosis, the ligase chain reaction assay had a sensitivity of 93.9%, a specificity of 99.8%, a positive predictive value of 83.8%, and a negative predictive value of 99.9%. CONCLUSIONS This study is the largest clinical trial to date to report the efficacy of the ligase chain reaction as a primary screening tool to detectMycobacterium tuberculosis infection. The authors conclude that ligase chain reaction is a useful primary screening test for tuberculosis, offering speed and discrimination in the early stages of diagnosis and complementing traditional smear and culture techniques.