Procuring rare (しい)* Japanese red blood cell units for a bleeding patient with anti-K11 requiring a life-saving procedure.

Alloimmunization to K11 is an extremely rare event. However, given the potential clinical significance of K11 alloantibodies, allocating antigen-negative red blood cell (RBC) units is a clinical necessity. In brief, we report a 39-year-old woman with multiple comorbidities including a right lower-extremity, below-the-knee amputation, who developed aggressive osteomyelitis associated with continuous bloody oozing, leading to anemia. To address these issues, the patient required extremity amputation. Surgery required addressing the concomitant critical anemia (hemoglobin <5 g/dL). However, with anti-K11 (in addition to anti-Jk^a) identified, no compatible units were immediately on hand and transfusing crossmatch-incompatible, antigen-positive units was deemed too high a risk. After a national search by the American Rare Donor Program (ARDP) was unsuccessful, the ARDP identified 2 irradiated, group O, K₀ (Kell_null), Jk(a-) RBC units in Japan that were predicted to be crossmatch-compatible with the patient's plasma. The units were successfully procured and infused, without evidence of adverse reactions, and the patient was able to safely undergo amputation to save her life. This case report reviews the complexities of anti-K11 detection and confirmation, as well as the processes by which K11- RBC units may be procured, which could help others in the global transfusion community should they be faced with similar challenging cases.