Plasma <i>Mycobacterium tuberculosis</i> cell-free DNA assay: a diagnostic tool for tuberculosis lymphadenitis

Background Bacterial confirmation in suspected tuberculosis lymphadenitis patients is challenging. This study evaluates plasma Mycobacterium tuberculosis cell-free DNA as a diagnostic tool for tuberculosis lymphadenitis. Methods A quantitative PCR assay targeting IS 6110 , IS 1081 , and cyp141 genes was performed on plasma samples. The study included 95 tuberculosis lymphadenitis patients and 60 controls. Sensitivity of the plasma Mycobacterium tuberculosis cell-free DNA assay was assessed against fine needle aspiration GeneXpert Ultra, fine needle aspiration culture, and fine needle aspiration cytology, while specificity was determined using control groups. Results Of the tuberculosis lymphadenitis cases, 71 (74.7%) were bacteriologically confirmed, and 24 (25.3%) were probable. In the control group, 50% had latent tuberculosis infection. The Mycobacterium tuberculosis cell-free DNA assay, targeting three genes, had an overall sensitivity of 65.3%, increasing to 70.4% for confirmed cases and 50% for probable cases, with specificity of 91.1%. Sensitivities for specific gene combinations were 62.1% for IS 6110 and IS 1081 , 54.7% for IS 6110 and cyp141 , and 55.8% for IS 1081 and cyp141 . For individual genes, IS 6110 showed 49.4% sensitivity (specificity: 93.3%), IS 1081 had 51.6% (specificity: 96.0%), and cyp141 showed 28.4% (specificity: 96.7%). Combining positive results from all three genes in the cell-free DNA assay with fine needle aspiration culture and GeneXpert Ultra improved sensitivity to 76.8% and 85.3%, respectively. Conclusion This study demonstrated that Mycobacterium tuberculosis cell-free DNA can be detected in the plasma of over half of tuberculosis lymphadenitis patients. The plasma Mycobacterium tuberculosis cell-free DNA assay could serve as a valuable, less-invasive complement to existing fine needle aspiration diagnostics.