title: Intensive red blood cell transfusions and risk of alloimmunization.
abstract: BACKGROUND
  Exposure to allogenic red blood cells (RBCs) may lead to formation of antibodies against nonself-antigens in transfused patients. While alloimmunization rates are known to increase with the number of transfusions, the transfusion course in patients can vary from receiving multiple units during a single transfusion event or getting them dispersed over a long(er) period. In this study we compared the immunization risk between different transfusion intensities.
  
  
  METHODS
  An incident new-user cohort study was conducted among consecutive transfused patients at two university medical centers. All patients who received their first RBC transfusion within the study period from January 2005 to December 2011 were eligible. Intensive transfusions were defined as at least 5, at least 10, and at least 20 RBC units within 48 hours. Alloimmunization hazard ratios (HRs), comparing patients receiving intensive transfusions to patients never receiving intensive transfusions, were estimated.
  
  
  RESULTS
  The study cohort was composed of 5812 patients who had received a median of 7 (interquartile range, 4-12) units. RBC alloantibodies were formed by 156 patients. The adjusted Cox regression HRs for alloimmunization, with number of units as the time covariate and adjusted for patient age, sex, and follow-up time after first transfusion, ranged from 0.8 to 1.2 (95% confidence interval, 0.4-2.6).
  
  
  CONCLUSIONS
  The occurrence of RBC alloimmunization in patients receiving intensive transfusions did not differ significantly from patients receiving nonintensive transfusions.
authors.affiliation: Center for Clinical Transfusion Research, Sanquin Research, Leiden, Netherlands; Department of Clinical Epidemiology, Jon J. van Rood Center for Clinical Transfusion Research, Leiden, Netherlands; Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, Netherlands; Department of Medical Statistics, Leiden University Medical Center, Leiden, Netherlands; Department of Clinical Chemistry and Haematology, University Medical Center Utrecht, Utrecht, Netherlands.
authors.forename: Saurabh
authors.initials: S
authors.lastname: Zalpuri
authors.forename: Rutger A
authors.initials: RA
authors.lastname: Middelburg
authors.forename: Henk
authors.initials: H
authors.lastname: Schonewille
authors.forename: Karen M K
authors.initials: KM
authors.lastname: de Vooght
authors.forename: Saskia
authors.initials: S
authors.lastname: le Cessie
authors.forename: Johanna G
authors.initials: JG
authors.lastname: van der Bom
authors.forename: Jaap Jan
authors.initials: JJ
authors.lastname: Zwaginga
mesh_terms: D000328:Adult; D000368:Aged; D001787:Blood Group Incompatibility / Q000453:epidemiology* / Q000276:immunology; D015331:Cohort Studies; D017707:Erythrocyte Transfusion / Q000009:adverse effects* / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007518:Isoantibodies / Q000097:blood*; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D012307:Risk Factors; D055815:Young Adult
chemical_list: D007518:Isoantibodies