Redefining MTBDR<I>plus</I> test results: what do indeterminate results actually mean?

Abstract

Early diagnosis of drug-resistant tuberculosis is critical in order to establish appropriate drug treatment regimens and to prevent the further transmission of resistant strains. Line probe assays (LPAs) are promising rapid diagnostics for use in low income settings, and can be used to screen smear-positive sputum samples for resistance to rifampicin (RIF) and isoniazid (INH) in as little as 1–2 days. Though the diagnostic performance of these assays has been well evaluated, little research has elucidated the true nature of indeterminate LPA results, or assessed the ability of these assays to perform on a wide range of clinical samples We evaluated the performance of the commercially available Genotype MTBDRplus LPA against conventional MGIT 960 culture and drug susceptibility testing (DST) results for 308 pulmonary (PTB) and 32 extrapulmonary (EPTB) tuberculosis samples. Invalid LPA results (defined as missing the MTB identification band) were obtained for 18 PTB samples, which were excluded from further analysis. The sensitivity and specificity of the Genotype MTBDRplus assay for multidrug-resistant tuberculosis (MDR-TB), based upon the results obtained for the remaining 322 samples, was 95.2% and 95.1%, respectively. 13.7% (40/290) of the PTB samples were not interpretable, or indeterminate, by LPA (defined as having the absence of both wild type and corresponding mutation bands) for INH and/or RIF and were further evaluated by pyrosequencing (PSQ). Contrary to standard LPA interpretation, INH and RIF susceptibility were confirmed by both DST and PSQ in 7.5% (3/40) and 27.5% (11/40) of indeterminate samples, respectively. When LPA test results were not interpretable in this study, PSQ was found to be a valuable and rapid technique to resolve discrepancies.

Multicenter evaluation of TB-SPRINT 59-Plex Beamedex®: accuracy and cost analysis

“…A large number of indeterminate results in TB SPRINT were observed, mainly for the analysis of mutations in the rpoB gene. These results were similar to other studies observed in MTBDR plus , [21–23]. In previous studies, regarding evaluation of the frequency of indeterminate results of TB-SPRINT, only accuracy was evaluated [9, 11].…”

Diagnostic Evaluation of Non-Interpretable Results Associated with rpoB Gene in Genotype MTBDRplus Ver 2.0

“…This finding of our study underscores that uncommon and/or silent mutation can cause NI results which can cause therapeutic dilemmas. Similarly, Nikam et al [ 23 ] observed NI results in both RIF and INH without mentioning any specific loci of genes in MTBDR plus assay. Their study also highlighted this limitation of LPA which is especially of concern in TB endemic areas.…”

MTBDRplus for the rapid diagnosis of ocular tuberculosis and screening of drug resistance

“…Although no such 'intermediate' results were obtained in the current study, prior studies have advised caution while interpreting results of MTBDRplus assay by confirming with sequencing. 28 The MTBDRplus assay has several advantages over other methods of DST. It is relatively simpler, faster and economical than conventional methods of DST.…”