Acute Hemolytic Transfusion Reaction due to Anti-P1: A Case Report and Review of Institutional Experience

<b>Background:</b> Here we report a case of acute hemolytic transfusion reaction (HTR) due to anti-P1 and review our institutional database for prevalence of anti-P1 antibodies and frequency of anti-P1-mediated HTR. Anti-P1 antibodies, reported to be present in up to two-thirds of P₂ individuals, are usually clinically insignificant. However, rare cases of acute HTR due to anti-P1 are reported. <b>Case Report:</b> We report the clinical and laboratory features of a mild acute HTR due to an IgM anti-P1 not detected by a routinely used antibody screening method. We reviewed our institutional database to investigate prevalence of anti-P1 antibodies identified in our patient population and frequency of HTR in patients with anti-P1. <b>Results:</b> Analysis of RBC transfusion recipient data over the 10-year period from 2006 to 2015 showed prevalence of anti-P1 identified in our laboratory of 174 per 100,000 individuals. Frequency of HTR in patients with anti-P1 identified in our laboratory over a 10-year period was 1 in 1,429 RBC transfusions (0.07%). <b>Conclusion:</b> Our reported case of HTR mediated by IgM anti-P1 reactive at 37 °C confirms the potential of antibody screening methods designed to detect IgG antibodies to miss rare clinically significant IgM antibodies.