A new strategy for the diagnosis of tuberculosis based on secreted antigens: evaluation of the efficacy of alveolar lavage ESAT-6 and CFP-10 tests.

OBJECTIVES: To assess the diagnostic value of Mycobacterium tuberculosis (MTB)-specific secreted antigens ESAT-6 and CFP-10 in bronchoalveolar lavage fluid (BALF), and to explore novel adjunctive diagnostic strategies to enhance the diagnostic rate of pulmonary tuberculosis (PTB).

METHODS: 104 patients with PTB (59 confirmed cases and 45 clinically diagnosed cases) and 72 patients with non-tuberculosis lung diseases (control group), hospitalized from May 2021 to July 2023, underwent bronchoscopy. The concentrations of ESAT-6 and CFP-10 antigens were detected by enzyme-linked immunosorbent assay (ELISA). Optimal cutoff values were determined by receiver operating characteristic (ROC) curves to evaluate antigen diagnostic capability for active PTB, compared with acid-fast bacilli (AFB) and Xpert MTB/RIF.

RESULTS: Antigen expression characteristics: Concentrations of ESAT-6 and CFP-10 were significantly higher in the PTB group compared to controls (both P&#x2009;<&#x2009;0.001). ESAT-6 levels did not differ significantly between confirmed and clinically diagnosed cases (P&#x2009;>&#x2009;0.05), whereas CFP-10 concentrations were significantly higher in confirmed cases (P&#x2009;=&#x2009;0.045). Comparison of diagnostic efficacy: Sensitivities of AFB and Xpert MTB/RIF were 26.92% (95% CI 18.6-37.2%) and 56.73% (95% CI 46.1-66.8%). ESAT-6 and CFP-10 demonstrated significantly higher sensitivities (77.89%, 95% CI 68.5-85.1%; 67.31%, 95% CI 57.3-76.0%) compared to AFB (&#x394;&#x2009;=&#x2009;50.97%, P&#x2009;<&#x2009;0.001; &#x394;&#x2009;=&#x2009;40.39%, P&#x2009;<&#x2009;0.001) and Xpert MTB/RIF (&#x394;&#x2009;=&#x2009;21.16%, P&#x2009;<&#x2009;0.001; &#x394;&#x2009;=&#x2009;10.58%, P&#x2009;=&#x2009;0.021), but had lower specificity (P&#x2009;<&#x2009;0.001). Combined testing strategy: Parallel testing (either antigen positive) yielded sensitivity of 94.23% (95% CI 87.4-97.6%) and negative predictive value of 99.2%, while tandem testing (both antigens positive) provided specificity of 95.83% (95% CI 88.1-98.6%). Subgroup analysis: No statistically significant difference was observed in antigen sensitivities between bacteriologically positive and negative PTB groups (P&#x2009;>&#x2009;0.05).

CONCLUSIONS: (1) ESAT-6 and CFP-10 detection in BALF significantly improves PTB diagnostic sensitivity, unaffected by bacterial load, particularly benefiting the diagnosis of bacteriologically negative PTB. (2) Combined antigen testing strategies (parallel/tandem) optimally balance sensitivity and specificity, meeting clinical requirements for ruling out or confirming PTB diagnosis.