The Effect of Rivaroxaban in Sickle Cell Disease

The primary study hypothesis is that inhibition of factor Xa with rivaroxaban will reduce inflammation, coagulation and endothelial cell activation, and improve microvascular blood flow in patients with sickle cell disease (SCD) during the non-crisis, steady state. To test this hypothesis, this study will evaluate the effects of rivaroxaban on: * plasma markers of inflammation; * plasma markers of endothelial activation; * plasma markers of thrombin generation; and * microvascular blood flow assessed using laser Doppler velocimetry (LDV) of post-occlusive reactive hyperemia (PORH). In a cross-over design, subjects will receive rivaroxaban 20 mg/day and placebo for 4 weeks each, separated by a 2-week washout phase.