ObjectiveTo analyze the results and diagnostic value of postoperative chylous test of pleural effusion and to verify the clinicopathological factors affecting the results of chylous test.MethodsThe clinical data of 265 consecutive patients undergoing selective surgery at the Department of Thoracic Surgery, Shangjin Nanfu Hospital between May and August 2020 were retrospectively analyzed, including 106 males and 159 females with an average age of 53.0±12.2 years. According to the results of the chylous test on the operation day and postoperative first and second days, the patients were divided into two subgroups, including a positive group and a negative group, and the clinical data of the two groups were compared. Sensitivity and specificity of the chylous test were calculated. The influencing factors for chylous test were analyzed by multiple logistic regression analysis.ResultsThe positive rate of chylous test was 91.7%, 95.8% and 87.9% on the operation day and postoperative first and second days, respectively. There was no statistical difference in age, sex, surgical type, surgical approach, surgical site, surgical time, degree of lymph node dissection, treatment of thoracic duct, 24 hours pleural fluid drainage or 24 hours protein and fat food intake between the positive group and the negative group (P>0.05). The diagnostic sensitivity and specificity of the chylous experiment were 100.0% and 4.0%, respectively. Multiple logistic regression analysis showed that the surgical site (left/right chest) might be an influencing factor for the results of the chylous test (P=0.043, OR=0.458, 95%CI 0.216-0.974).ConclusionThe positive rate of chylous test of pleural effusion after thoracic surgery is very high. The chylous test produces a high misdiagnosis rate of chylothorax. The surgical site (left/right chest) may be an influencing factor for chylous test. The positive result of chylous test is not recommended as the direct diagnostic basis for postoperative chylothorax and guidance of the subsequent treatment.