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

Objective: To assess the diagnostic value of Mycobacterium tuberculosis (MTB)-specific secreted antigens ESAT-6 and CFP-10 in alveolar 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 cut-off 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<0.001). ESAT-6 levels did not differ significantly between confirmed and clinically diagnosed cases (P>0.05), whereas CFP-10 concentrations were significantly higher in confirmed cases (P=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%), respectively, with specificity at 100%. 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 (Δ=50.97%, P<0.001; Δ=40.39%, P<0.001) and Xpert MTB/RIF (Δ=21.16%, P<0.001; Δ=10.58%, P=0.021), but had lower specificity (P<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>0.05). Conclusion: (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.