Resistance of sickle whole blood clots to tPA-mediated fibrinolysis is transiently prevented by RBC exchange in sickle patients. CLT of clots formed from PPP (A) or whole blood (B) of AA subjects (n = 8-9), AS (n = 11), and SCD (n = 13-15). Effect of tPA at 0.625 nM (C) and 1.25 nM (D) concentration on the CLT of clots formed from the whole blood of AA control subjects, SS patients, or SS patients undergoing RBC Ex pre- and postprocedure (n = 15). The values for the AA and SS groups. (C-D) The first 2 bars are copied from panel B. Effect of restoring PLT number in postexchange sample on CLT (E), whole blood PLT number (F), and serum levels of total (G) and active PAI-1 (H). All 4 parameters were analyzed in an independent cohort of sickle cell patients undergoing RBC exchange (n = 9-14), which was different from that used for the data presented in panels C and D. *P < .05, ** P< .01, ***P < .001.