Figure 1. Time course of serial hematocrit measurements of a trauma patient who presented with a major scalp laceration and abdominal injuries and received four units of red cells during the initial phase of treatment.

At 6 days later, his hematocrit again decreased and a new anti-Jk(a) red cell alloantibody was noted. Approximately three-quarters of Caucasian donors are Jk(a) antigen-positive and retained segments of the blood bag tubing tested positive for Jk(a) in three of the four units administered. The patient hemolyzed these three units with a nine-point drop in his hematocrit. He was then uneventfully transfused with Jk(a) antigen-negative red cells.

RBC: Red blood cell; U: Unit.