Effects of agonist-induced activation on platelets from patients with SCD or healthy participants. (A) ADP reactivity of platelets from patients with SCD and PAH. The curves represent the mean percentage plus or minus SEM of activated platelets (activated GPIIb/IIIa) after their incubation with increasing concentrations of ADP. Patients with SCD and secondary pulmonary hypertension (SCD + PAH; ▲) reached higher degrees of activation with significantly lower concentrations of ADP compared with control participants (■) and patients with SCD without PAH (SCD − PAH; ●). (B) Reactivity of platelets from patients with SCD and PAH to activation by TRAP is compared with that of platelets from healthy control participants or patients with SCD without PAH.