Comparative evaluation of loop-mediated isothermal amplification (LAMP) assay, GeneXpert MTB/Rif and multiplex PCR for the diagnosis of tubercular lymphadenitis in HIV-infected patients of North India

Background Tubercular lymphadenitis (TBLA) is one of the most common extrapulmonary manifestations of tuberculosis in patients with HIV. With several other pathological conditions presenting as lymphadenitis and lack of consensus regarding a gold standard test, the diagnosis of TBLA remains a challenge for the clinician. Objectives: and design: In this study, we have assessed the potential of loop-mediated isothermal amplification (LAMP) test for the diagnosis of TBLA in HIV-infected patients. The study group included samples collected by fine needle aspiration (FNAC) of lymph nodes from 24 HIV-infected patients with TBLA. A composite reference standard was used to identify cases of TBLA based on clinical suspicion, results of cytology, AFB smear, MGIT culture, GeneXpert MTB/RIF, multiplex polymerase chain reaction (MPCR) and subsequently clinical response to antitubercular therapy. These tests were also carried out in 26 control samples of lymph node FNAC from HIV-infected patients with non-tubercular lymphadenitis. Results: LAMP assay was positive in 19/24 TBLA cases and yielded a sensitivity of 79.17% with 100% specificity. Cytology was suggestive in 18/24 (75%) TBLA cases. GeneXpert MTB/RIF assay correctly identified 16/24 TBLA cases, but the test did show one false positive result reducing its specificity. MPCR had the highest sensitivity of 91.67% as it correctly identified 22/24 cases and showed no false positive result. Conclusion: The current study highlights the potential of LAMP test for the specific diagnosis of tubercular lymphadenitis in FNAC samples from HIV-infected patients, especially when cytology is either non-conclusive or non-available. Though MPCR had a higher sensitivity than LAMP assay, the added advantages of low cost, minimal technical expertise and simplicity of procedure make LAMP assay a suitable diagnostic test in resource-limited settings.