75 ABO Discrepancy with distinct mixed field reaction on forward typing in a pediatric acute myeloid leukemia patient

ABO discrepancies can be observed with hematologic malignancies such as acute myeloid leukemia (AML). In these situations, there can be a loss or diminished expression of red blood cell (RBC) antigen seen in the forward typing and subsequent re-expression of original RBC antigen after remission is achieved. An 11-year-old female presented with 6-day history of nausea, migratory pain, decreased appetite, daily low-grade fevers, ecchymoses and leukocytosis of over 547 K/uL. The initial ABO typing showed mixed field group A in forward and group A in reverse. There is no evidence of prior transfusion history. Consequently, patient’s ABO typing was initially reported as unspecified while awaiting molecular testing results. ABO genotyping was performed by Sanger sequencing on exons 2-7, including the intronic flanking regions, of the ABO gene (SeqStudio genetic analyzer, Thermo Fisher Scientific, USA) which revealed the patient’s genotype as ABO*A1.01/O.01.01 with predicted phenotype of group A. She was diagnosed with AML with monosomy 7 and started on induction therapy with cytarabine, hydrocortisone and methotrexate. In the setting of unresolved mixed field, the patient received 10 units of group O RBC prior to ABO genotyping result and subsequently 17 units of group A RBC during her hospital course. This is a rare case that demonstrates a distinct mixed field reaction on forward type before the diagnosis of AML in a pediatric patient with no prior transfusion history.