Transfusion of buffy coat‐depleted blood components and risk of postoperative infection in orthopedic patients

Volume 40, March 2000 TRANSFUSION 381 Transfusion of buffy coat-depleted blood components and risk of postoperative infection in orthopedic patients Innerhofer et al.1 reported an association between the transfusion of buffy coat-poor allogeneic RBCs and postoperative infection from a carefully conducted, prospective observational study of 385 orthopedic surgery patients. This association was still significant (p = 0.003) following adjustment for the effects of advanced age, female sex, low body weight and height, and transfusion of FFP. Twenty-seven of the 34 recorded infections were urinary tract infections (UTIs); an association between allogeneic RBC transfusion and postoperative UTI was thus observed, which had not been noted previously in the randomized controlled trials that reported an increased postoperative infection rate among the recipients of WBC-containing allogeneic blood components.2-4 Nosocomial UTIs are associated, for the most part, with urinary catheters, and urinary catheters are implicated in 80 percent of nosocomial UTIs in the United States.5 In the retrospective observational study by Vamvakas et al.6 of allogeneic transfusion and postoperative infection in patients undergoing elective colorectal cancer resection, the association between allogeneic transfusion and postoperative UTI disappeared after adjustment for the effects of the number of days with indwelling urinary catheter, the presence of chronic systemic illness, and female sex. Only these three variables had a significant effect on postoperative UTI in that study,6 but Innerhofer et al.1 presented statistical adjustment for only one of them (i.e., female sex). It is possible that a policy for universal WBC reduction may be implemented in the United States in the near future, as it has been implemented in Canada and several western European countries.7 Should this happen, further investigation of the purported, deleterious, immunomodulatory effects of allogeneic transfusion will have to rely on observational studies, because random assignment of patients to WBC-reduced transfusion and non-WBC-reduced transfusion arms will no longer be possible.7 Attention thus must be focused on designing observational studies correctly, as the credibility of these reports depends on the adequacy of the presented adjustment for the effects of confounding factors.7 Because the number of days with indwelling urinary catheter is by far the predominant risk factor for postoperative UTI,5,6 an observational study can detect an association between allogeneic transfusion and postoperative UTI only if it adjusts statistically for the effect of that risk factor. The purported, deleterious, immunomodulatory effects of allogeneic transfusion are most important for developing rational perioperative transfusion practices, and optimal use should be made of all the available data sets to prove (or disprove) the existence of these adverse effects of allogeneic transfusion.8 For this reason, it is essential to know whether the association reported by Innerhofer et al.1 will persist after adjustment for the effect of the number of days with indwelling urinary catheter. Even if this information was not collected by the authors during the study period, it is available in the medical records and can be retrieved retrospectively. Because the authors state, “A Foley urinary catheter was inserted before surgery and usually removed on the morning of the second postoperative day,”1(p626) the reporting of these adjusted results will be of great interest. It is to be hoped that the authors will consider re-analyzing their data, after including the information on this important confounding factor. Eleftherios C. Vamvakas, MD, PhD Department of Pathology New York University Medical Center New York, NY 10016 e-mail: stephen.vamvakas@med.nyu. edu