BACKGROUND

Red blood cell (RBC) transfusion has been related to thromboembolic events. Microvesicles in the RBC product may support coagulation because they have procoagulant effects in vitro. We investigated whether transfusion of RBCs containing extracellular vesicles promotes coagulation in human recipients. As transfusion is mostly administered to ill patients, we used a model of endotoxemia.

STUDY DESIGN AND METHODS

Eighteen healthy volunteers were randomized to receive either saline or fresh (2 days stored) or stored autologous (35 days stored) RBC transfusion (Dutch Trial Register: NTR4455). Two hours after infusion of lipopolysaccharide (LPS, from Escherichia coli, 2 ng/kg body weight), subjects received either saline or fresh or stored RBCs. Blood was sampled every 2 hours up to 8 hours after LPS infusion. Vesicles were measured with a flow cytometer (A50-Micro, Apogee Flow Systems).

RESULTS

LPS resulted in increased thrombin generation compared to baseline. During storage, the total number of extracellular vesicles increased from 1.4 × 10 /mL (interquartile range [IQR], 8.3 × 10 -1.9 × 10 /mL) in the fresh product to 1.7 × 10 /mL (IQR, 7.9 × 10 -2.3 × 10 /mL; p < 0.01) in the stored product (p < 0.001). Vesicles appeared to be mostly RBC derived.

CONCLUSION

After transfusion, extracellular vesicles from stored RBC products, but not from fresh products, could be detected in the circulation of healthy volunteers. However, infusion of stored RBC extracellular vesicles did not augment thrombin generation compared to endotoxemic controls. Also, levels of d-dimer and thrombin-antithrombin complex were unaffected. In conclusion, transfusion of autologous RBCs containing high levels of extracellular vesicles does not enhance coagulation in human volunteers with endotoxemia.