Evaluation of kit-based loop-mediated isothermal amplification (TB-LAMP) assay in the diagnosis of tubercular lymphadenitis

Background: The rapid and accurate diagnosis of tubercular lymphadenitis remains a challenging task today.WHO endorsed LoopAMP™ MTBC kit (TB-LAMP) as a replacement for sputum-smear microscopy in the diagnosis of pulmonary tuberculosis (PTB). However, no prospective diagnostic accuracy study of TB-LAMP in tubercular lymphadenitis in adults has been done yet. Current study evaluated the diagnostic performance of TB-LAMP in tubercular lymphadenitis (LNTB).Material & Methods: In a prospective observational study conducted at a tertiary care hospital in India, 90 subjects (age>18years) suspected of LNTB were consecutively recruited and followed up till six months between January 2019 and December 2020. Samples were processed for microscopy, culture, GeneXpert®, histopathology and TB-LAMP. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of TB-LAMP against composite reference standard (CRS) and culture were determined.Results : TB-LAMP showed a sensitivity of 83.78% (95% CI, 73.76-90.47) and specificity of 81.25% (95% CI, 56.99-93.41) respectively against CRS. The PPV and NPV were 95.38% (95% CI, 87.29-98.42) and 52.00% (95% CI, 33.50-69.97) respectively. TB-LAMP showed a sensitivity of 88.89% (95% CI, 71.94-96.15) and specificity of 36.17% (95% CI, 23.97-50.46) respectively against culture. The PPV and NPV were 44.44% (95% CI, 32-57.62) and 85% (95% CI, 63.96-94.76) respectively.Conclusion: TB-LAMP can be used over conventional microscopy for the diagnosis of TB in lymph node specimens at primary health care centres. This is the rapid and cost-effective diagnosis of LNTB in resource-limited settings due to good sensitivity and NPV.