Center for Clinical Transfusion Research, Sanquin, Leiden, Netherlands; p.vandermeer@sanquin.nl. Department of Hematology, HagaZiekenhuis, The Hague, Netherlands. Dept. of Medical Statistics and Bioinformatics, Leiden University Medical Center, Leiden, Netherlands. Center for Clinical Transfusion Research, Sanquin, Leiden, Netherlands. Department of Immunohematology and Blood bank, Leiden University Medical Center, Leiden, Netherlands. Department of Hematology, HagaZiekenhuis, The Hague, Netherlands. Department of Immunohematology and Blood bank, Leiden University Medical Center, Leiden, Netherlands. Juravinsky Hospital, Hamilton, Canada. Hematology, Maastricht University Medical Center, Maastricht, Netherlands. Hematology, Erasmus Medical Center, Rotterdam, Netherlands. Ottawa Hospital, Ottawa, Canada. Department of Clinical Pathology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada. Department of Medicine, Division of Hematology, London Health Sciences Center, London, ON, Canada. Kingston General Hospital, Kingston, Canada. Immunology, Blood Systems Research Institute, San Francisco, CA, United States. Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO, United States. Center for Clinical Transfusion Research, Sanquin, Leiden, Netherlands. Haukeland University Hospital, Bergen, Norway. Medicine, McMaster University, Hamilton, ON, Canada. Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, Netherlands. Department of Hematology, HagaZiekenhuis, The Hague, Netherlands.