Evaluation of direct detection of Mycobacterium tuberculosis in clinical samples using the BD ProbeTec ET system

OBJECTIVE: To evaluate the performance of the semi-automated BD ProbeTec ET system for the direct detection of Mycobacterium tuberculosis complex (MTBC) in comparison with microscopy, and culture for respiratory and non-respiratory specimens.

METHODS: The study was conducted in the Maternity and Children's Hospital, Madina, Saudi Arabia from October 2008 to October 2009. A single center prospective study of 70 suspected tuberculosis samples were subjected to microscopy, culture (solid and liquid), and the DB ProbeTec ET system.

RESULTS: A total of 70 specimens were studied; 47 respiratory, and 23 non-respiratory. Twelve (92.3%) ProbeTec positive results were obtained from 13 MTBC isolates from culture, while one specimen was BD ProbeTec ET positive, but yielded no growth on culture. Two samples gave anomalous results (false negative and positive results). The evaluated system showed sensitivity of 92.3%, specificity of 98%, positive predictive value of 92.3%, and negative predictive value of 98% for all specimens, while 88% sensitivity, 100% specificity, 100% positive predictive value, and 97.3% negative predictive value in cases of respiratory specimens, and 100% sensitivity, 93.3% specificity, 80% positive predictive value, and 100% negative predictive value in cases of non-respiratory specimens.

CONCLUSION: The ProbeTec ET is a rapid and specific method for direct detection of MTBC in clinical specimens compared with the gold standard of culture, especially in patients with smear-negative non-respiratory specimens.