Performance of the BD ProbeTec ET direct detection assay for the analysis of Mycobacterium tuberculosis in respiratory and non-respiratory clinical specimens

Objectives: Early detection of Mycobacterial tuberculosis infection (MTB) is pivotal for the treatment of tuberculosis (TB). Background: This study was performed to evaluate the performance of BD ProbeTec ET direct detection assay (DTB) against the gold standard culture technique for confirmation of MTB infection. Methods: A total of 266 consecutive and non-duplicate clinical specimens for detection of MTB were included in this study. There were 118 respiratory and 148 non-respiratory samples. All samples were tested by microscopy for acid-fast bacillus (AFB), MTB culture and biochemical identification with simultaneous testing by DTB. Results: A total of 88 samples (33%) were culture-positive for MTB including 39/118 respiratory, 29/99 fluid and 20/49 tissue samples. DTB sensitivity for respiratory samples was 97% and specificity was 96% with a positive predictive value (PPV) of 93% and negative predictive value (NPV) of 99%. Sensitivity of DTB in fluid samples was 80%, specificity 88%, PPV 69% and NPV 93% whereas sensitivity of DTB for tissue samples was 25%, specificity 90%, PPV 63% and NPV 63%. Of the 50 (56.8%) smear-positive samples, DTB sensitivity was 100% for respiratory, 85% for fluid and 100% for tissue samples. Conclusion: DTB performed within acceptable limits for the rapid detection of MTB in respiratory samples compared to fluid and tissue specimens.