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

Background-The ligase chain reaction Mycobacterium tuberculosis assay uses ligase chain reaction technology to detect tuberculous DNA sequences in cli nical specimens. A study was undertaken to determine its sensitivity and sp ecificity as a primary screening tool for the detection of culture positive tuberculosis. Methods-The study was conducted on 2420 clinical specimens (sputum, broncho alveolar lavage fluid, pleural fluid, urine) submitted for primary screenin g for Mycobacterium tuberculosis to a regional medical microbiology laborat ory. Specimens were tested in parallel with smear, ligase chain reaction, a nd culture. Results-Thirty nine patients had specimens testing positive by the Ligase c hain reaction assay. Thirty two patients had newly diagnosed tuberculosis, one had a tuberculosis relapse, three had tuberculosis ton antituberculous therapy when tested), and three had healed tuberculosis. In the newly diagn osed group specimens were smear positive in 21 cases (66%), ligase chain re action 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 posit ive 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 detect Mycobacterium tuberculosis infection. The authors conclude that ligase cha in reaction is a useful primary screening test for tuberculosis, offering s peed and discrimination in the early stages of diagnosis and complementing traditional smear and culture techniques.