A Preliminary Study to Compare TB-LAMP Assay and GeneXpert MTB/RIF for Diagnosis of Pulmonary Tuberculosis

Abstract

Tuberculosis is a major public health problem. The gold standard technique for diagnosis of active tuberculosis is detection of Mycobacterium tuberculosis (MTB) by culture, which takes 3-8 weeks due to
a slow growth rate of the bacilli. Molecular method by nucleic acid amplification technique (NAAT) is an alternative method to detect MTB- specific nucleic acid which provide higher sensitivity, more specificity in a very short time compared to culture. This preliminary study was to compare the performance of molecular techniques for detection the MTB DNA in suspected patient’s sputum by Isothermal amplification
(TB - LAMP) and GeneXpert. Three catagories of 74 tested samples from previous testing left over sputums were included in this study : Group 1 was 16 samples from AFB positive sputum with three positive grading results (Scanty, 1+, 2+ and 3+). Group 2 included 53 negative AFB sputums. Group 3 were 5 positive MTB sputums by GeneXpert MTB/RIF. The results revealed that group 1 sample showed positive results by both methods (100 % concordance). Among group 2 of 53 AFB negative, 27 sputums were found to be positive by Xpert MTB/RIF and 17 were positive by TB-LAMP, demonstrated 50.9 % and 32.1 % increment, respectively. Group 3 gave 5 positive results of TB-LAMP test methods (100 % concordance). In comparison, among 74 samples Xpert MTB/ RIF detected 48 positive while TB-LAMP found 38 positive MTB (79% concordance). The results demonstrated that TB-LAMP could detected MTB in 17 of 53 negative AFB samples with 32 % increment . Therefore, implementing of TB-LAMP which is much cheaper cost and less time consume compared to Xpert MTB/RIF for detecting MTB in AFB negative will be able to reduce using Xpert MTB/RIF testing by at least 79 %, leading to more effectiveness for TB control and prevention.

Key words: TB, Xpert MTB/RIF, TB-LAMP