A Rare Case of P-Null Phenotype Identified During Preoperative Screening.

A 46-year-old woman scheduled for an elective total abdominal hysterectomy was incidentally found to have a rare P-null (p) phenotype during routine preoperative testing. Although her ABO/Rh type was A positive, the antibody screen demonstrated strong pan-reactivity with all panel cells, while the autocontrol was negative, indicating an alloantibody. This prompted referral to a reference immunohematology laboratory, where the pan-agglutinating antibody was ultimately identified as specific anti-P1Pk, consistent with the patient's rare P-null phenotype. Consequently, the patient was flagged as requiring future transfusions with P-null, ABO/Rh-compatible red blood cells. Surgery proceeded without the need for transfusion, but identification of this rare phenotype has substantial implications for long-term care, particularly given the known association of anti-PP1Pk with severe hemolytic transfusion reactions and recurrent pregnancy loss. This case highlights the importance of comprehensive pretransfusion testing, early collaboration with specialized laboratories, meticulous documentation, and proactive transfusion planning, particularly in regions where such phenotypes may be underrecognized.