Switching donor cells as a major source of error in compatibility testing

The most likely cause of fatality in blood transfusion is transfusion of the wrong unit of blood to a patient. This type of error is usually attributed to improper patient identification at the time of sample collection or transfusion. A retrospective analysis of the results of an external proficiency testing program identified a common source of error occurring during laboratory testing that has not been previously reported. Results were analyzed when major errors were assigned to laboratories for obviously switching donor units in compatibility testing and/or subsequent investigation. In 24 surveys sent to extended testing (Level A) laboratories and 18 sent to basic testing (Level B) laboratories, the antigenic composition of the two donor cells made it possible to determine whether the cells had been switched. Seven errors were assigned to Level A participants for switching donor units during testing, constituting 38.9 percent of the 18 major errors assessed. Level B participants were assigned eight errors for switching donor units, 26.7 percent of the 30 major errors assessed. Approximately one-third (31.3 percent) of major errors committed on 42 proficiency testing surveys were caused by switching of donor cells during compatibility testing. This type of error may result in transfusion of an incompatible donor unit.