Effect of MPs on plasma clotting time. MP aliquots from patients with sickle cell disease could shorten plasma clotting time, whereas similar MP aliquots from healthy subjects could not (P = .001). Parallel samples (▪) show that MP shortening of plasma clotting time could be partially inhibited by a TF antibody, demonstrating TF-dependent procoagulant activity (P = .002). Error bars represent SEM.