Clinical Evaluation of BDProbeTec ET Direct TB Assay for Detection of Mycobacterium tuberculosis Complex in Respiratory and Non-Respiratory Specimens

Kim, Soo Young; Park, Yeon Joon; Kim, Byung Kee

Abstract

BACKGROUND
Recently developed BDProbeTec ET direct TB assay (BDET; Becton Dickinson, Sparks, MD, USA) uses strand displacement amplification in which DNA segments of the IS6110 are amplified and detected by a fluorescent energy transfer. In this study, we evaluated the performance of the BDET for direct detection of Mycobacterium tuberculosis complex (MTBC) in respiratory and non-respiratory specimens by comparing results with those of COBAS AMPLICOR MTB assay (CAS: Roche, Basel, Switzerland) and Mycobacteria growth indicator tube (MGIT) in a clinical setting.
METHODS
A total of 281 (152 respiratory and 129 non-respiratory) specimens collected from 253 patients were tested in parallel with three assays. The results were evaluated in combination with both MGIT cultures and clinical data set to the so-called "gold standard".
RESULTS
Forty specimens (14.2%) were from patients with tuberculosis, and thirty specimens (10.7%) were culture positive for MTBC. The level of agreement between cultures, CAS, and BDET was 87.2%. The sensitivities, specificities, and the positive and negative predictive values for respiratory specimens were 69.2%, 100%, 100%, and 94.0%, respectively, for CAS, and 76.9%, 92.9%, 69.0%, and 95.1%, respectively, for BDET. The same values for non-respiratory specimens were 42.9%, 100%, 100%, and 93.5%, respectively, for CAS, and 100%, 93.0%, 63.6%, and 100%, respectively, for BDET. CAS was significantly more specific than BDET with both respiratory (P=0.002) and non-respiratory (P=0.004) specimens and BDET was far more sensitive than CAS for non-respiratory specimens (P=0.001). CONCLUSTIONS: Considering the low sensitivities of other available tests, BDET is a potentially excellent diagnostic tool for diagnosis of extra-pulmonary tuberculosis.