ObjectiveTo explore the impacts of eliminated erythrocyte on morphological alterations of tumour cells in hemorrhagic effusion from NSCLC carcinoma and the pretreatment application of gene mutation detection by low-osmosis method.MethodsData of 24 cases of hemorrhagic effusion from NSCLC carcinoma patients in the Affiliated Hospital of Putian University from march 2018 to march 2019 were collected.Cytologic blocks were prepared with paraffin-embedding by low-osmosis to remove RBCs.We used mixture of 50% ethanol and 10% neutral buffer formalin(NBF)to damages RBCs and conventional way to form a paraffin-embedded cytologic block in control group.H-E and nucleic acid extraction evaluations were performed.ResultSignificantly decreased RBCs, higher number of tumor cells, clearly and more distinct cellular outlines were significantly different with low-osmosis method than the conventional method(P<0.05).There was no obvious difference compared to the mixture of 50% ethanol and 10% NBF(P>0.05).The qualification rate of nucleic acids-both DNA and RNA-by low-osmosis method was noticeably different than that of the conventional method(P<0.05).Thirteen nucleic acid mutations were detected in 24 cases screened for EGFR mutations while EML4-ALK and ROS1 gene fusion were not detected.ConclusionThe results indicate that the low-osmosis method is an efficient way to dispose the hemorrhagic effusion from NSCLC carcinoma and it is able to support the genetic testing related to target therapy of NSCLC.