1. Division of Hematology, Children's Hospital of Philadelphia, Philadelphia, PA;
2. Department of Pathology & Laboratory Medicine, and
3. Division of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA;
4. Department of Clinical Chemistry & Hematology and Cell Microscopy Center, University Medical Center Utrecht, Utrecht, The Netherlands; and
5. Division of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA