title: A systematic review of the effect of red blood cell transfusion on mortality: evidence from large-scale observational studies published between 2006 and 2010.
abstract: OBJECTIVE
  To carry out a systematic review of recently published large-scale observational studies assessing the effects of red blood cell transfusion (RBCT) on mortality, with particular emphasis on the statistical methods used to adjust for confounding. Given the limited number of randomised trials of the efficacy of RBCT, clinicians often use evidence from observational studies. However, confounding factors, for example, individuals receiving blood generally being sicker than those who do not, make their interpretation challenging.
  
  
  METHODS
  Systematic review.
  
  
  METHODS
  We searched MEDLINE and EMBASE for studies published from 1 January 2006 to 31 December 2010.
  
  
  METHODS
  We included prospective cohort, case-control studies or retrospective analyses of databases or disease registers where the effect of risk factors for mortality or survival was examined. Studies must have included more than 1000 participants receiving RBCT for any cause. We assessed the effects of RBCT versus no RBCT and different volumes and age of RBCT.
  
  
  RESULTS
  -32 studies were included in the review; 23 assessed the effects of RBCT versus no RBCT; 5 assessed different volumes and 4 older versus newer RBCT. There was a considerable variability in the patient populations, study designs and level of statistical adjustment. Overall, most studies showed a higher rate of mortality when comparing patients who received RBCT with those who did not, even when these rates were adjusted for confounding; the majority of these increases were statistically significant. The same pattern was observed in studies where protection from bias was likely to be greater, such as prospective studies.
  
  
  CONCLUSIONS
  Recent observational studies do show a consistently adverse effect of RBCT on mortality. Whether this is a true effect remains uncertain as it is possible that even the best conducted adjustments cannot completely eliminate the impact of confounding.
authors: Systematic Review Initiative, NHS Blood and Transplant, Department of Haematology, Oxford University Hospitals and University of Oxford, Oxford, UK.
authors: Sally
authors: S
authors: Hopewell
authors: Omar
authors: O
authors: Omar
authors: Chris
authors: C
authors: Hyde
authors: Ly-Mee
authors: LM
authors: Yu
authors: Carolyn
authors: C
authors: Doree
authors: Mike F
authors: MF
authors: Murphy
keywords: Epidemiology; Intensive & critical care
references: J Orthop Trauma. 2006 Nov-Dec;20(10):675-9
references: 17106377
references: World J Surg. 2008 Oct;32(10):2185-9
references: 18575931
references: Anesthesiology. 2012 Jun;116(6):1367-76
references: 22487863
references: Crit Care Med. 2006 Jun;34(6):1608-16
references: 16607235
references: Shock. 2007 Aug;28(2):165-71
references: 17529904
references: J Trauma. 2008 Aug;65(2):279-82; discussion 282-4
references: 18695462
references: J Trauma. 2008 Oct;65(4):794-8
references: 18849793
references: Transfusion. 2006 Oct;46(10):1712-8
references: 17002627
references: Ann Thorac Surg. 2006 May;81(5):1650-7
references: 16631651
references: Br J Anaesth. 2012 Jun;108(6):943-52
references: 22593128
references: Interact Cardiovasc Thorac Surg. 2010 Jan;10(1):37-42
references: 19815567
references: Health Technol Assess. 2003;7(27):iii-x, 1-173
references: 14499048
references: Am Heart J. 2006 Dec;152(6):1028-34
references: 17161047
references: Lancet. 2013 May 25;381(9880):1845-54
references: 23706801
references: Crit Care Med. 2008 Sep;36(9):2667-74
references: 18679112
references: J Trauma Manag Outcomes. 2008 Oct 20;2(1):9
references: 18937866
references: Am J Cardiol. 2008 Jul 15;102(2):115-9
references: 18602505
references: Transfusion. 2008 Feb;48(2):237-50
references: 18005329
references: Transfusion. 2010 Jun;50(6):1185-95
references: 20158690
references: JAMA. 2012 Oct 10;308(14):1443-51
references: 23045213
references: Crit Care Med. 2006 Sep;34(9):2302-8; quiz 2309
references: 16849995
references: JACC Cardiovasc Interv. 2009 Jul;2(7):624-32
references: 19628185
references: Crit Care. 2008;12(2):R60
references: 18442375
references: Anesthesiology. 2009 Aug;111(2):327-33
references: 19625800
references: Transfus Med Rev. 2011 Apr;25(2):145-155.e2
references: 21345644
references: Circulation. 2007 Nov 27;116(22):2544-52
references: 17998460
references: Cochrane Database Syst Rev. 2007 Apr 18;(2):MR000005
references: 17443628
references: J Am Coll Surg. 2009 May;208(5):931-7, 937.e1-2; discussion 938-9
references: 19476865
references: Ann Thorac Surg. 2009 Jul;88(1):95-100, 100.e1-3
references: 19559202
references: Ann Intern Med. 2011 Jul 5;155(1):39-51
references: 21727292
references: Am Surg. 2007 Jan;73(1):1-5
references: 17249446
references: Transfusion. 2005 Sep;45(9):1523-30
references: 16131387
references: BMC Med. 2009 Jul 31;7:37
references: 19646221
references: N Engl J Med. 2008 Mar 20;358(12):1229-39
references: 18354101
references: Anesthesiology. 2008 Jan;108(1):31-9
references: 18156879
references: Clin Cardiol. 2007 Oct;30(10 Suppl 2):II49-56
references: 18228652
references: Ann Surg. 2010 Jul;252(1):11-7
references: 20505504
references: JAMA. 2010 Oct 13;304(14):1568-75
references: 20940382
references: BMC Musculoskelet Disord. 2009 Dec 29;10:167
references: 20040083
references: Arch Intern Med. 2008 Nov 24;168(21):2377-81
references: 19029504
references: Ann Thorac Surg. 1998 Jan;65(1):125-36
references: 9456106
references: Am J Crit Care. 2009 Mar;18(2):124-31; quiz 132
references: 19255102
references: J Vasc Surg. 2010 Mar;51(3):616-21, 621.e1-3
references: 20110154
references: Transfus Apher Sci. 2010 Aug;43(1):107-16
references: 20655807
references: Transfus Med Rev. 2011 Jul;25(3):197-205
references: 21550205
references: Anesth Analg. 2009 Jun;108(6):1741-6
references: 19448195
references: Vox Sang. 2011 Jan;100(1):46-59
references: 21175655
references: Am Heart J. 2009 Oct;158(4):653-8
references: 19781427