Diagnostic accuracy of loop-mediated isothermal amplification assay for extra-pulmonary tuberculosis in Indian population.

Background: Confirmatory diagnosis of extra-pulmonary tuberculosis remains a true challenge owing to difficulty in procuring appropriate specimen, inefficient laboratory methods and paucibacillary nature of infection. These obstructions become all the very difficult in pediatric EPTB cases, due to non-specific clinical signs and symptoms, low sensitivity of smear microscopy and culture, lack of awareness among clinicians, etc. AIM OF THE STUDY: The present study aimed to evaluate the diagnostic accuracy of rapid and cost-effective loop-mediated isothermal amplification (LAMP) assay for EPTB diagnosis in children.

Methods: A total of 154 cases were analyzed by EPTB-site smear microscopy, culture, PCRs for IS6110, MPB64 & Pab genes, nested PCR and LAMP assay. Single-gene PCRs were performed by custom-synthesized primers. Nested PCR was performed using the 3B BIOTUB Kit and the LAMP assay was done using the Nu-LAMP TB kit.

Results: We observed that the molecular tests displayed 4-fold higher positivity rate (minimum 46%) in comparison to the microbiological tests (maximum 11.03%). In contrast to the composite reference standard, LAMP assay was found to be 79.6% sensitive and 78% specific for EPTB diagnosis in childhood cases.

Conclusions: Our results indicate that LAMP assay is a promising technique for efficient diagnosis of EPTB in children belonging to resource-limited regions.