Abstract: An apparatus and method of its use to prevent accidental transfusion of mismatched blood types from a blood bag containing pre-typed blood to a patient. The system includes two major independent but mating components: 1) a cannula spike attached to a cannula adapted for intravenous infusion of a fluid from the bag into a patient and 2) a plurality of different individual receptacle ports of graduated size, of which at least one is selectively attached to the outside of pilot tube at the time of blood typing. The cannula spike is a connected series of decreasingly sized individual cannula spike units, each unit being configured to be matingly received by and uniquely coded to its matching female receptacle port. Each of the units is individually removable from the cannula spike and the last unit may be affixed permanently to the cannula. Each unit may also be color coded, bar coded, and affixed with linear indicia to assist the user in avoiding an accidental mismatch between blood types.