Comparative evaluation of loop-mediated isothermal amplification and conventional methods to diagnose extrapulmonary tuberculosis

Abstract

Background: Extra-pulmonary tuberculosis is difficult to diagnose by conventional methods, because they are less sensitive and more time consuming. Loop-mediated Isothermal Amplification (LAMP) is a novel gene amplification method that has been developed to diagnose Mycobacterium tuberculosis complex in pulmonary and paucibacillary extrapulmonary specimens even in resource poor settings. Aims and Objectives: To evaluate the sensitivity and specificity of LAMP to detect Mycobacterium tuberculosis complex in paucibacillary extra-pulmonary specimens and to compare the results with other conventional methods in extrapulmonary specimens. Materials and Methods: 45 specimens from suspected extrapulmonary tuberculosis patients were collected and tested by LAMP method after DNA extraction. Simultaneously, these specimens were tested by smear microscopy, solid and liquid culture methods. Culture positivity, either in solid or liquid culture, was considered as a confirmed case of extrapulmonary tuberculosis. Results: Sensitivity of LAMP was 95.6% whereas for liquid culture, solid culture and smear microscopy were 69.6%, 65.2% and 17.4% respectively. Specificity for LAMP was 95.4% and for other 3 conventional methods were 100%. Positive predictive values, negative predictive values and likelihood ratios were also evaluated. Turn-around time (TAT) for LAMP was 8 hours only whereas for liquid culture was 2-4 weeks, and for solid culture it was 4-8 weeks. Conclusion: LAMP was a simple, rapid and cost-effective procedure with good sensitivity and specificity. It was found to be better than conventional methods to diagnose extrapulmonary tuberculosis.