MMP3 and Pleural effusion: The AUC of pleural effusion pleural effusion MMP-3 combined with serum MMP-3 in the differential diagnosis of PEE was 0.810 (95% CI 0.716–0.904), the AUC of pleural effusion pleural effusion CYFRA21-1 combined with serum CYFRA21-1 in the differential diagnosis of PEE was 0.822 (95% CI 0.724–0.920), the AUC of pleural effusion ADA combined with serum ADA in the differential diagnosis of PEE was 0.836 (95% CI 0.747–0.924), and the AUC of the three combined differential diagnosis PEE was 0.923 (95% CI 0.868–0.978).