Summary

Primary haemostasis is mediated by platelet aggregation. Red blood cells (RBCs) are involved in this process. We hypothesised that stored RBCs could have less capacity to support primary haemostasis. This was tested with RBC units from 17 healthy volunteers stored for 45 days. Fresh citrated blood was taken again from the same donors and platelet-rich plasma was prepared, in which RBCs were resuspended with a constant haematocrit (40%), but changing fractions of stored versus fresh autologous RBCs (0, 25, 50, 75, and 100%, respectively). A platelet function analyser PFA-100® was used. In this instrument blood is aspirated through a membrane pore coated with collagen and either epinephrine (EPI) or ADP, which causes platelets to adhere, aggregate, and form an occluding plug, which stops blood flow and is measured as closure time (CT). We found that the CT increased with increasing fractions of stored blood. CT-EPI was 121 ± 17 seconds [s], 129 ± 32 s, 164 ± 45 s (p< 0.000, ANOVA), 214 ± 54 s (p< 0.0001), and 273 ± 36 s (p< 0.0001) for 0, 25, 50, 75, and 100% stored RBCs. For CT-ADP the values were 91 ± 22 s, 95 ± 12 s, 101 ± 13 s, 124 ± 44 s (p= 0.004), and 191 ± 72 s (p< 0.0001), respectively. We conclude that stored RBCs have less capacity than normal RBCs to support primary haemostasis by platelet aggregation in vitro, suggesting a decreased capacity of stored RBCs to bring platelets into close contact with the wall, which may contribute to sustained bleeding seen after mass transfusion.