Sensitivity and specificity of loop-mediated isothermal amplification assay for diagnosis of extra-pulmonary tuberculosis: A cross-sectional study

Abstract

Introduction: Extra-pulmonary tuberculosis (EPTB) accounts for 15-20% of total TB cases in India. Many cases remain undiagnosed due to low sensitivity or long turn-around-time of conventional diagnostic tests. Molecular tests offer rapidity and improved sensitivity with exquisite specificity, but they are expensive, require skilled manpower or enhanced laboratory infrastructure. Loop-mediated isothermal amplification assay (LAMP) assay is a unique, temperature-independent DNA amplification test facilitated by visual optic readout. WHO recommended use of LAMP for pulmonary TB (2016). For END TB strategy to succeed, it is necessary to capture EPTB early and start them on effective therapy. Aims and Objectives: To determine sensitivity & specificity of TB-LAMP assay for diagnosis of EPTB against culture and Xpert MTB/RIF assay Methods: In a cross-sectional study, 100 consecutive EPTB specimens were processed for microscopy, culture, Xpert and LAMP assay. Results: 100 specimens included in the study were body fluids(65), pus(19) & tissue(16). TB was detected in 38 specimens by any of the 4 methods. Positivity of microscopy was 5%, culture 28%, Xpert 25% & LAMP 32%. Sensitivity & specificity of LAMP against culture was 85.71% & 88.89% and against Xpert was 88% & 86.67% respectively. LAMP detected TB in 32 specimens of which 24 were culture positive & 22 were Xpert positive. 8 patients were only LAMP positive; 4 of them were put on anti-TB treatment based on clinical-radiological diagnosis. Conclusion: LAMP has good sensitivity & specificity in EPTB specimens. Further studies are required to establish utility of LAMP as a diagnostic tool for EPTB.