P-Null Phenotype Due to a Rare Frame-Shift Mutation and with Allo-Anti-PP1Pk Causing a Severe Hemolytic Transfusion Reaction: A Case Report with Clinical Management.

Introduction: The identification of alloantibodies to high-frequency antigens (HFA) and subsequent transfusion management can be challenging and often poses a problem in finding the compatible blood for transfusion. The aim of this study was to investigate the specificity of the antibody to the HFA causing a hemolytic transfusion reaction (HTR) and procure the compatible blood unit for future transfusion.

Case Presentation: A 4-year-old female met with a head injury that led to intracranial bleeding and surgical intervention was required to remove blood clots. In the face of anemia, blood transfusion was planned. The pretransfusion tests on her blood sample revealed the presence of a pan-reactive alloantibody with hemolytic properties. She was transfused with 10 mL of the least incompatible red blood cells (RBCs) to which she reacted with signs of clinical hemolysis, i.e., chill, rigor, fever, and hemoglobinuria, on 3 different occasions. Despite her anemia, she was managed by medical intervention only. Her antibody reacted with all RBCs tested, except autologous and P-null (p phenotype) cells. Her RBCs did not react with anti-PP1Pk, which corroborated her phenotype as P-null. The genomic study revealed she was hemi- or homozygous or for a deletion of 26-bp in exon 3, previously reported as causing the P-null phenotype and designated *

Conclusion: This report documents a rare case of the P-null phenotype with an alloanti-PP1Pk causing a severe HTR to transfusion of the trial dose of the least incompatible blood. The case is the first example of this specific mutation found in India.