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. The World Health Organization (WHO) endorsed the 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 for tubercular lymphadenitis in adults has been performed yet. The current study evaluated the diagnostic performance of TB-LAMP in tubercular lymphadenitis (LNTB).

METHODS: In a prospective observational study conducted at a tertiary care hospital in India, 90 subjects (age >18 years) suspected of LNTB were recruited consecutively and followed up for 6 months between January 2019 and December 2020. Samples were processed for microscopy, culture, GeneXpert, histopathology and TB-LAMP. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of TB-LAMP against the composite reference standard (CRS) and culture were determined.

RESULTS: TB-LAMP showed a sensitivity of 83.78 % (95 % CI, 73.76-90.47) and a specificity of 81.25 % (95 % CI, 56.99-93.41), respectively, against the 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 a 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 instead of conventional microscopy for the diagnosis of TB in lymph node specimens at primary healthcare centres. It provides rapid and cost-effective diagnosis of LNTB in resource-limited settings due to good sensitivity and NPV.