There is a growing body of evidence that transfusion alters host defenses against infection. A meta-analysis of randomized controlled trials demonstrated that a restrictive approach to red blood cell (RBC) transfusion decreases the risk of infection by 24%. This evidence has prompted changes in guidelines for the use of RBC transfusion. The objective of this investigation was to examine whether transfusion affects the risk of developing a bloodstream infection from a urinary source.