ObjectiveTo investigate the relationship between the nodule manifestation of malignant pleural lesions under medical thoracoscopy and pleural fluid biochemistry and tumor marker levels. MethodsA total of 110 patients with malignant pleura, including 90 cases of lung cancer, 18 cases of malignant mesothelioma, 1 case of diffuse large B-cell lymphoma, and 1 case of ovarian serous carcinoma, who were hospitalized in the Department of Respiratory and Critical Care Medicine, East Hospital of Shandong Provincial Hospital from February 2011 to January 2022 were selected as the study subjects. The pleural nodule manifestation was divided into 6 layers were according to the number of pleural nodules in the medical thoracoscopic field, they were divided into 6 layers: non-nodular group, nodular group (pleural nodules of different sizes were distributed); The nodular group was further divided into nodular scattered group (total number of pleural nodules in all fields under thoracoscopy ≤10) and nodular diffuse group (total number of pleural nodules in all fields under thoracoscopy >10); The nodular diffuse group was further divided into the multiple nodules diffused group (the total number of pleural nodules >10 under thoracoscopy and ≤10 nodules in a single microscopic field) and the nodular diffuse patchwork group (the total number of pleural nodules >10 under thoracoscopy and >10 nodules in a single microscopic field). Four biochemical items of pleural fluid, pleural fluid lactate dehydrogenase (LDH), adenosine deaminase (ADA), glucose (GLU), protein quantification (TP) levels and pleural fluid carcinoembryonic antigen (CEA), carbohydrate antigen 125 (CA125) levels, serum CEA, and serum cytokeratin fragment 19 (CYFRA21-1) levels were measured to compare the expression levels of indicators between the non-nodular group and the nodular group, the nodular scattered group and the nodular diffuse group, the multiple nodules diffused group and the nodular diffuse patchwork group.ResultsThe LDH level in pleural fluid of nodular group was significantly higher than that of non-nodular group (P<0.01). The LDH level in pleural fluid of diffuse nodular group was higher than that of scattered nodular group (P<0.05). Compared to those in multiple nodules diffused group, the levels of LDH and ADA in pleural fluid of nodules patchy diffused group were significantly increased (P<0.01), and the GLU level was decreased (P<0.05). However, there were no statistically significant differences in the length of disease, smoking index, TP in pleural fluid, CEA in pleural fluid, CA125 in pleural fluid, CEA in serum and CYFRA21-1 in serum between the paired groups.ConclusionsThere were differences in the expression levels of LDH, ADA and GLU in pleural fluid of different degrees of malignant pleural lesions. The higher the degree of pleural lesions, the higher the levels of LDH and ADA in pleural fluid and the lower the levels of GLU in pleural fluid.