Intraoperative auto-transfusion with the use of cell saver systems is routinely used to reduce the rate of packed red blood transfusion in major surgery. Nevertheless some concerns have been raised on possible risks of coagulation disorders. The aim of the study was to analyze the blood processed by the cell saver, ready to be re-infused to the patient, in order to individuate unexpected cellular components, that can favor coagulopathy. We tested the blood processed by the cell saver in thirteen patients undergoing coronary bypass surgery with Cellsearch®, ScreenCell®, Cytology and Immunofluorescence. Those four methods allowed us to look for the presence of unexpected cells, quantify and characterize them. Furthermore, the blood processed by the cell saver was mixed with the patient’s peripheral blood and analyzed with the ROTEM® thromboelastography. The Cellsearch® revealed and counted a mean number of 1241 unexpected cells/7.5 ml in the blood processed by the cell saver. The ScreenCell® and Cytology confirmed the presence of non-hematological cells. Immunofluorescence showed positivity for Calretinin and WT-1, confirming the mesothelial origin. Moreover we detected a peculiar arrangement of the platelets around the mesothelial cells in a “cloud” form, suggesting platelet activation. The ROTEM® analysis showed a significantly longer clot formation time, smaller clot amplitude and maximum clot firmness, compared to controls. In conclusion we demonstrated the presence of mesothelial cells in the cell saving blood, ready to be auto-transfused. This finding can contribute to develop a platelet depletion coagulopathy, with coagulation factors consumption.