title: Transfusion of stored red blood cells in trauma patients is not associated with increased procoagulant microparticles.
abstract: BACKGROUND
  We set out to determine the effects of transfusing stored red blood cells (RBCs) on the levels of procoagulant microparticles (MPs) in the blood of trauma patients.
  
  
  METHODS
  Blood was drawn and processed to platelet poor plasma for MP analysis for 409 injured patients seen in the trauma bay from February 2011 to January 2013. Blood from 27 noninjured volunteers was also analyzed. Quantification of total procoagulant MP (per microliter plasma) using a direct plasma analysis via flow cytometry was performed. Demographic data, Injury Severity Score (ISS), overall mortality, and units of transfused packed RBCs were collected. Data are presented as median (interquartile range [IQR]). Transfusion groups were assessed using t test or Wilcoxon rank-sum test as appropriate. The α level was set as 0.05 for statistical significance.
  
  
  RESULTS
  Median ISS was 12 (IQR, 5-19), 12% were transfused, median age was 48 years (IQR, 29-62 years), 68% were male, and overall mortality was 3%. Median units transfused were 3 (IQR, 2-5). The median number of all procoagulant MP was greater in trauma patients (median 758; IQR, 405-1,627) when compared with our control subjects (median, 232; IQR, 125-372; p < 0.0001). This difference remained significant after adjusting for age and sex (p < 0.0001). In 39 patients who had MP levels measured before transfusion with RBC, the procoagulant MP levels did not change after transfusion (p = 0.07). Patients transfused with RBCs that were 14 days or older did not have increased procoagulant MP levels when compared with those that received RBCs that were younger than 14 days (p = 0.5).This was also true for those who received RBCs that were 28 days or older when compared with those that received RBCs that were younger than 28 days (p = 0.84).
  
  
  CONCLUSIONS
  Procoagulant MP is significantly greater in trauma patients as compared with volunteers, even after adjusting for age and sex. We did not observe any change in the levels of procoagulant MPs after transfusion of stored RBCs.
  
  
  METHODS
  Epidemiologic/prognostic study, level III.
authors.affiliation: From the Departments of Trauma and Critical Care Surgery (S.K.D., M.L.H., D.H.J., M.S.P.), Health Sciences Research (J.K.R., W.S.H.), and Hematology Research (T.M.H.), Mayo Clinic, Rochester. Minnesota.
authors.forename: Satbir K
authors.initials: SK
authors.lastname: Dhillon
authors.forename: Mindy L
authors.initials: ML
authors.lastname: Houck
authors.forename: Donald H
authors.initials: DH
authors.lastname: Jenkins
authors.forename: Jordan K
authors.initials: JK
authors.lastname: Rosedahl
authors.forename: William S
authors.initials: WS
authors.lastname: Harmsen
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Halling
authors.forename: Myung S
authors.initials: MS
authors.lastname: Park