National Journal of Laboratory Medicine (Jan 2018)
Role of Line Probe Assay for Rapid Detection of Mycobacterium tuberculosis Complex and Drug Resistance Directly from Clinical Samples
Abstract
Introduction: The global burden of Multi Drug Resistant Tuberculosis (MDR TB) is increasing worldwide. Smear microscopy has low sensitivity, culture based tests for identification of tubercle bacilli and drug susceptibility testing take weeks to give results. Molecular tests allow rapid detection of Mycobacterium tuberculosis Complex (MTBC) and drug resistance in 4-8 hours. Real-time-PCR based GeneXpert provides only RIF susceptibility. In this study newer GenoType MTBDRplus VER 2.0 assay is utilized which gives sensitivity of both the first line anti-tubercular drugs. Aim: To evaluate the performance of Line Probe Assay (LPA) for rapid identification and detection of drug resistance in MTBC in respiratory and non-respiratory samples. Materials and Methods: All the samples (respiratory and non-respiratory) received from clinically suspected cases of Tuberculosis (TB), admitted in various wards, ICUs and outdoor patients of Dayanand Medical College and Hospital during the study, were processed in the Department of Microbiology. Samples other than Cerebro Spinal Fluid (CSF) were digested and decontaminated by NALC-NaOH method. Microscopy by ZN (Ziehl-Neelsen) staining, liquid culture by MGIT (Mycobacterial Growth Indicator Tube, BD BBLTM), and LPA by the GenoType MTBDRplus assay, VER 2.0, HAIN Life Science) were performed on all the samples. Results: A total of 70 samples were considered which includes 34 respiratory samples and 36 non-respiratory samples. Out of the 70 samples, 13 (18.6%) were smear positive, 23 (32.8%) grown in culture and 29 (41.4%) were detected positive for MTBC by LPA. Considering culture as gold standard the sensitivity, specificity, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) of the LPA for diagnosis of TB in respiratory and non-respiratory samples were found as (83.33%, 72.73%), (72.73%, 80%), (62.5%, 61.54%) and (88.89%, 86.96%) respectively while sensitivity of LPA in smear positive and smear negative samples were found as 90% and 69.23% respectively. All the samples except two showed sensitivity to Isoniazid (INH) and Rifampicin (RIF). Two samples were found resistant to INH only. Conclusion: LPA performed directly on samples is a wonderful tool for fast detection of MTBC in the respiratory samples along with INH and RIF resistance. In comparison, the sensitivity of LPA is less in non-respiratory samples. Still, many patients can be diagnosed and can start appropriate treatment till the culture report is received.
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