Intraoperatively salvaged red blood cells contain nearly no functionally active platelets, but exhibit formation of microparticles: results of a pilot study in orthopedic patients

BACKGROUND: Previous data show improved clot formation after retransfusion of salvaged red blood cells (RBCs). This study was conducted to explore whether such RBCs contain clinically relevant numbers of active residual platelets (PLTs) or exhibit formation of microparticles (MPs). STUDY DESIGN AND METHODS: Thirteen patients undergoing major orthopedic surgery were included in the study, and arterial blood samples from patients and samples from the retransfusion bag were analyzed with various PLT function tests and flow cytometry. RESULTS: With commercial blood cell counters, the numbers of PLTs in the RBC unit were reduced to approximately 25% compared to patients' blood. In contrast, results from flow cytometry showed an 11‐ to 945‐fold reduction in median counts referring to total PLTs and free PLTs. Interestingly, smaller quantities of PLT‐derived MPs were found in samples from the retransfusion bag than in patients' arterial blood. Conversely, RBC‐ and white blood cell–derived MP counts were increased in the retransfusion bag compared to the patient. Rotational thrombelastometry and the Impact‐R system (DiaMed) showed a pronounced impairment of PLT ability with regard to adhesion, aggregation, and clot formation. With the use of confocal microscopy, only a few free thrombocytes were detectable among the huge numbers of RBCs. CONCLUSION: Only few free and thus active PLTs are detectable in processed RBCs. It seems very unlikely that these few PLTs can improve clot strength. Nevertheless, the impact of the detected MPs on thrombin generation needs to be clarified in further studies.