In situ thrombin generation influences clot stability. Clots were formed by incubating cells with recalcified normal, pooled PFP in the presence of tPA (250 ng/mL) and clot formation and lysis were monitored by an increase and subsequent decrease in turbidity at 405 nm. All values for (A) time to peak and (B) peak turbidity (± SD) were statistically different (*P < .05) compared with HUVECs.