Redefining MTBDRplus test results: what do indeterminate results actually mean?
OBJECTIVE: To evaluate the performance of the commercially available GenoType® MTBDRplus LPA against conventional BACTEC™ MGIT™ 960 culture and drug susceptibility testing (DST) among 308 pulmonary tuberculosis (PTB) and 32 extra-pulmonary TB samples.
RESULTS: Invalid LPA results (defined as those with a missing Mycobacterium tuberculosis identification band) were obtained for 18 PTB samples, which were excluded from further analysis. The sensitivity and specificity of the MTBDRplus assay for multidrug-resistant TB, based upon the results obtained for the remaining 322 samples, was respectively 95.2% and 95.1%. Of 290 PTB samples, 40 (13.7%) were indeterminate on LPA (defined as the absence of both wild-type and corresponding mutation bands) for isoniazid (INH) and/or rifampicin (RMP), and were further evaluated by pyrosequencing (PSQ). Contrary to standard LPA interpretation, INH and RMP susceptibility were confirmed by both DST and PSQ in respectively 7.5% (3/40) and 27.5% (11/40) of indeterminate samples.
CONCLUSION: PSQ was found to be a valuable and rapid technique to resolve discrepancies in LPA test results that were not interpretable.
Document Type: Research Article
Affiliations: 1: *Department of Microbiology, P D Hinduja Hospital and Medical Research Centre, Mumbai, India 2: †Department of Medicine, University of California San Diego, La Jolla, California, USA
Publication date: February 1, 2016
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