The influence of platelets, plasma and red blood cells on functional haemostatic assays

Functional whole blood haemostatic assays are used increasingly to guide transfusion therapy and monitor medical treatment and are also applied for in-vitro evaluations of the haemostatic potential of stored platelets. We investigated how the cellular and plasmatic elements, both isolated and combined, influenced the two methodologically different assays, thrombelastography (TEG) and impedance aggregometry (Multiplate). Platelet-rich plasma (200 × 10/l) or pure plasma (0 platelets), with and without added red blood cells (RBCs), hematocrit 0, 0.15 or 0.29, were produced in vitro from platelet concentrates, fresh frozen plasma and stored RBC. Pure platelets were investigated by removing plasma components from platelet concentrates by diafiltration against the platelet storage solution Intersol. Plasma was readded by diafiltration against plasma in Intersol. Haemostatic function was evaluated by TEG and Multiplate. In the TEG, increasing amounts of RBC reduced clot strength and clot kinetics (α-angle), most markedly in plasma/RBC without platelets. In contrast, RBC in a platelet concentrate matrix enhanced Multiplate aggregation in response to weak agonists (ADP and arachidonic acid). Furthermore, removing plasma from platelet concentrates eliminated the TEG response and diminished the Multiplate aggregation response, but readding plasma to the pure platelet concentrates restored the response. Each of the elements in whole blood, plasma, platelets and RBC, affected the Multiplate and TEG results differently. The results emphasize that the concentrations of all cellular and plasmatic components in whole blood should be taken into account when interpreting results obtained by TEG and multiplate.