Abstract Introduction/Objective Introduction: The Kell blood group system, discovered in 1946, holds paramount significance in transfusion medicine and hemolytic disease of the newborn (HDN). Named after Mrs. Kelleher, who exhibited anti-Kell antibodies resulting in HDN, this system comprises 25 antigens, with the original K antigen retaining primary importance. Additionally, Levine et al. identified anti-Cellano, now known as anti-k, presenting an antibody antithetical to anti-K. Methods/Case Report Case Presentation: A 60-year-old male with a history of bioprosthetic aortic valve insufficiency, pulmonary homograft stenosis, and recurrent aortic insufficiency presents for a fourth redo sternotomy for root and ascending aorta replacement. Preoperative assessment revealed a positive antibody screen for anti-k, a clinically significant antibody associated with decreased survival of transfused red blood cells (RBCs). Given limited compatible blood units available, efforts are underway to secure additional donations before the scheduled surgery on 2/22/24. The patient’s medical history indicates no recent blood transfusions or iron therapy, with the last transfusion in 1996. He is anticoagulated with warfarin for mechanical valve and atrial fibrillation, necessitating preoperative bridging with Lovenox injections. Methods The patient’s antibody screen and initial panel demonstrated pan-reactivity with 3+ reactivity, suggesting an antibody targeting a high-frequency antigen. Further testing using polyethylene glycol (PEG) confirmed the presence of anti-k, supported by negative reactions to additional K-negative cells. The absence of other clinically significant antibodies was verified using 0.2 M Dithiothreitol (DTT) modified cells. Results (if a Case Study enter NA) NA Conclusion Conclusion: The identification of anti-k antibody underscores the critical role of preoperative antibody screening in mitigating transfusion-related complications, particularly in patients requiring complex surgical interventions. Collaborative efforts between clinical teams and transfusion medicine specialists are imperative to ensure adequate blood product availability and optimize patient outcomes.To prevent further exposure, it is recommended that patients with rare antibodies carry an Antibody ID card indicating the rare antibody they possess.k antigen blood donors are underrepresented in the general donor pool. It is recommended to develop a systematic recruitment for k antigen donors.