Evaluation of the TB-LAMP assay for the rapid diagnosis of pulmonary tuberculosis in Northern India.

Setting: A tertiary care hospital in North India.

Objective: To evaluate a commercial kit-based loop-mediated isothermal amplification (TB-LAMP) assay for the diagnosis of pulmonary tuberculosis (PTB).

Design: A total of 530 patients presenting with PTB symptoms were enrolled and one sputum sample was collected from each patient. The TB-LAMP assay (Loopamp™ MTBC Detection kit) was performed on the raw sputum sample. The remaining sample was used for smear microscopy and mycobacterial culture. A cartridge-based nucleic acid amplification test (NAAT, Xpert® MTB/RIF assay) was also performed on the processed pellet.

Results: The sensitivity and specificity of the TB-LAMP assay in culture-positive samples obtained from 453 patients presenting with PTB symptoms (77 specimens were excluded) were respectively 100% (95%CI 94.7-100) and 99.2% (95%CI 97.8-99.8). The sensitivity and specificity of Xpert in culture-positive samples were respectively 82.6% (95%CI 71.5-90.6) and 94.9% (95%CI 92.2-96.8). A concordance of 0.75 was obtained between the two NAATs (TB-LAMP assay and Xpert) using the κ statistic.

Conclusion: The TB-LAMP assay showed high sensitivity and specificity with limited requirement of testing infrastructure, and is thus a promising diagnostic tool for TB diagnosis in resource-poor settings.