Evaluation of a commercial ligase chain reaction assay for the diagnosis of pulmonary and extra-pulmonary tuberculosis

SETTING: Egas Moniz Hospital, Lisbon, Portugal. OBJECTIVE: TO evaluate the Ligase Chain Reaction (LCx(R)) Mycobacterium tub erculosis Assay for the direct detection of M. tuberculosis complex in resp iratory specimens after smear observation, and its suitability for non-resp iratory clinical specimens. DESIGN: Analysis of 156 specimens collected fro m 123 patients with pulmonary tuberculosis and/or extrapulmonary involvemen t. RESULTS: Among 93 pulmonary secretions and 63 extra-pulmonary samples and a fter resolution of discrepancies based on clinical and laboratory findings, two pulmonary samples from a patient with a diagnosis of sarcoidosis, four samples of cerebrospinal and one of seminal fluid were considered as false positives. Two tis-sue biopsy samples, one pericardial effusion and one pu lmonary secretion from patients strongly suspected of having tuberculosis w ere considered as false negatives for the assay, without inhibition of ampl ification. All specimens yielding M. avium on culture were LCx negative. CONCLUSION: The LCx(R) Mycobacterium tuberculosis Assay was found to be use ful for the rapid identification of M. tuberculosis complex in all types of specimens. It revealed a high specificity both in pulmonary and extrapulmo nary products, and a sensitivity of 97% for the pulmonary secretions and of 75% for the extra-pulmonary specimens, independently of the bacilloscopy r esults.