[1] St Christophers Hosp Children, Marian Anderson Comprehens Sickle Cell Ctr, Philadelphia, PA 19134 USA
[2] Drexel Univ, Coll Med, Dept Pediat, Philadelphia, PA 19104 USA
[3] Thomas Jefferson Univ, Sch Med, Dept Pediat, Philadelphia, PA 19107 USA
[4] Ctr Comprehens Sickle Cell, Stat & Data Management Ctr, Rho Fed Syst Div, Chapel Hill, NC USA