1. From the Department of Surgery, School of Medicine, University of Pennyslvania, Philadelphia (J.H.C., N.G., L.H.E.); the Sol Sherry Thrombosis Research Center, Hematology Division, Departments of Medicine and Physiology, Temple University, Philadelphia, Pa (A.K.R., R.W.C.); and the Department of Pathology and Laboratory Medicine, University of California, Los Angeles (T.A.D.).