| Summary: | In patients presenting for liver transplantation, increased platelet aggregation as well as thrombocytopenia have been demonstrated, but bedside assays have not been investigated. We compared platelet aggregation in liver transplantation patients and control surgical patients using impedance aggregometry. We hypothesized that platelet activity is not altered during liver transplantation. After the allowance of the ethics committee, platelet aggregation was determined using impedance aggregometry with the activators ristocetin, adenosine diphosphate (ADP), arachidonic acid, collagen, and thrombin receptor-activating peptide (TRAP) in liver transplantation patients at four time points (start of surgery, anhepatic phase, reperfusion, end of surgery) and in control surgical patients. Moreover, platelet count was determined using a Coulter counter. To compensate for the thrombocytopenia often present in patients presenting for liver transplantation, the ratio between impedance aggregometry finding and platelet count was used. For statistical evaluation, the <i>t</i>-test or the Mann−Whitney U-test were used, as appropriate. Platelet aggregation ratio showed a 3.1-fold increase in liver transplantation patients (<i>n</i> = 37) in comparison to control surgical patients (<i>n</i> = 10) when ristocetin was used as the activator (<i>p</i> = 0.001). Moreover, an approximately twofold increase of ADP-, arachidonic acid-, collagen-, and TRAP-induced platelet aggregation ratio was determined. Platelet aggregation normalized at the end of the transplantation procedure. Impedance aggregometry revealed a markedly increased platelet aggregation in some liver transplantation patients and might be suitable to guide platelet transfusion and antiplatelet therapy.
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