title: Emergency transfusion of patients with unknown blood type with blood group O Rhesus D positive red blood cell concentrates: a prospective, single-centre, observational study.
abstract: BACKGROUND
  Emergency patients with unknown blood type usually receive O Rhesus D negative (RhD-) red blood cell concentrates until their blood group is determined to prevent RhD+ related adverse transfusion reactions. As 85% of individuals are RhD+, this consumption of O RhD- red blood cell concentrates contributes to shortages of O RhD- red blood cell concentrates, sometimes forcing transfusion of known RhD- patients with RhD+ red blood cell concentrates. Here we report the outcome of this transfusion policy transfusing all emergency patients with unknown blood type with O RhD+ red blood cell concentrates.
  
  
  METHODS
  In this prospective single-centre observational study done between Jan 1, 2001, and Dec 31, 2015, we assessed all consecutive RhD- patients at the University Medicine Greifswald who received RhD+ red blood cell concentrates (emergency patients with unknown blood type; and RhD- patients receiving RhD+ red blood cell concentrates during RhD- red blood cell concentrate shortages). No patients were excluded. The primary endpoint was anti-D allo-immunisation at 2 months follow-up or later. Patients were followed up and tested for immunisation against red blood cell antigens using the direct antiglobulin test and an antibody screen every 3-5 days for 4 weeks or until death, or hospital discharge. Surviving patients were screened for development of anti-D antibodies for up to 12 months (at the predefined timepoints 2, 3, 6, and 12 months) after RhD+ red blood cell transfusion.
  
  
  RESULTS
  437 emergency patients, of whom 85 (20%) were RhD-, received 2836 RhD+ red blood cell concentrates. The overall risk of inducing anti-D antibodies (in all 437 recipients) was 17 (4%, 95% CI 2·44-6·14) of 437 (assuming all patients lost to follow-up developed anti-D allo-immunisation). During this period, 110 known RhD- patients received RhD+ red blood cell concentrates during RhD- red blood cell concentrate shortages. Of these, 29 (26%; 95% CI 19·0-35·3) developed anti-D allo-immunisation (assuming all patients lost to follow-up developed anti-D), which was significantly higher than in the emergency patients with unknown blood type (p<0·0001).
  
  
  CONCLUSIONS
  Transfusing emergency patients with unknown blood type with O RhD+ red blood cell concentrates has a low risk of inducing anti-D antibodies (3-6%), but saves more than 10% of the total O RhD- red blood cell concentrate demand, thereby reducing shortage of O RhD- red blood cell concentrates, the need to transfuse known RhD-patients with RhD+ red blood cell concentrates, and thus the overall risk to induce anti-D allo-immunisation in the population. These findings should be considered for transfusion guidelines.
  
  
  BACKGROUND
  University Medicine Greifswald.
authors.affiliation: Department of Immunology and Transfusion Medicine, University Medicine Greifswald, Germany.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Selleng
authors.affiliation: Department of Immunology and Transfusion Medicine, University Medicine Greifswald, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Jenichen
authors.affiliation: Department of Immunology and Transfusion Medicine, University Medicine Greifswald, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Denker
authors.affiliation: Department of Anesthesiology, University Medicine Greifswald, Germany.
authors.forename: Sixten
authors.initials: S
authors.lastname: Selleng
authors.affiliation: Department of Anesthesiology, Heart and Diabetes Center of Mecklenburg and Western Pommerania, Karlsburg, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Müllejans
authors.affiliation: Department of Immunology and Transfusion Medicine, University Medicine Greifswald, Germany. Electronic address: greinach@uni-greifswald.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Greinacher
mesh_terms: D000368:Aged; D001789:Blood Group Antigens / Q000276:immunology; D001803:Blood Transfusion / Q000379:methods* / Q000401:mortality; D003298:Coombs Test / Q000379:methods; D004638:Emergency Treatment; D017707:Erythrocyte Transfusion / Q000379:methods*; D004912:Erythrocytes / Q000502:physiology*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011446:Prospective Studies; D018029:Rho(D) Immune Globulin / Q000276:immunology* / Q000627:therapeutic use
chemical_list: D001789:Blood Group Antigens; C061961:RHO(D) antibody; D018029:Rho(D) Immune Globulin