Abstract: Objective:To compare the difference of routine marker expression level in patients with different causes of hydrothorax and ascites,and to explore the value of differential diagnosis. Method:606 cases of hospitalized patients in Yingshan People's Hospital from October 2013 to April 2017 were enrolled,including 461 cases of hydrothorax(176 cases of general pleural effusion,152 cases of malignant pleural effusion,133 cases of tuberculous pleural effusion)and 145 cases of ascites(80 cases of general ascites,63 cases of malignant ascites,2 cases of tuberculous ascites).For the samples of hydrothorax and ascites,total protein(TP),adenosine deaminase(ADA),glucose(GLU),lactate dehydrogenase(LDH),chloride(CL)and C reactive protein(CRP) were detected,and Rivalta test,cell counting and classification were made.The test results were statistically analyzed. Result:The level of TP,ADA,CRP,positive rate of Rivalta test and percentage and absolute counting of mononuclear cells in tuberculous pleural effusion group were significantly higher than those in other groups(all P<0.05),and the proportion of bloody pleural effusion in patients with malignant pleural effusion was significantly higher than that in other groups(P<0.05).The level of TP,ADA,LDH,CRP and positive rate of Rivalta test in malignant ascites were significantly higher than those in general ascites(all P<0.05),while glucose level was significantly lower than that in general ascites(P<0.05).The ROC curve showed a number of indicators including ADA could be used for differential diagnosis of tuberculous pleural effusion[The area under ROC curve(AUC)more than 0.70],and combined use with multi index could significantly improve the diagnostic efficiency(AUC was 0.946);while TP,LDH and CRP could be used for differential diagnosis of malignant ascites and general ascites,but single and combined use of different indicators were of limited value(AUC only slightly more than 0.70).Conclusion:Several commonly used laboratory indicators are valuable for differential diagnosis of pleural and ascitic fluid,especially through the combined application of multiple indicators,which can significantly improve the diagnostic efficiency of tuberculous pleural effusion.