Wisconsin Diagnostic Laboratories Milwaukee, Wisconsin, United States
Background/Case Studies: ABO antigens are the most clinically significant antigens due to their immunogenicity. ABO incompatibilities are a cause of serious clinical consequences and as such, ABO typing is a foundation of safe pretranfusion testing and is critical in pretransplantation workups. Blood banks most commonly rely on serological testing for these antigens, but it is not always definitive. The use of molecular testing provides a more unequivocal result. Serological testing will detect variations in antigen expression that molecular testing will not.
Study
Design/Methods: A 21yo American Indian presented to an outside hospital (OSH) in October 2022 with a two-week history of a sore throat and cough. The patient developed diarrhea and symptoms progressed with bilateral lower extremity swelling, generalized weakness, vomiting, easy bruising, petechiae, and weight loss. This OSH typed the patient as O positive without issue. The patient was transfused 2 platelets, 2 plasma, and 2 pRBCs and transferred out. At the second OSH, the patient was diagnosed with Chronic Myelomonocytic Leukemia-2 (CMML-2) and chemotherapy was initiated. The patient again typed as O positive by solid phase testing without issue on the first two samples tested at the second OSH in October 2022. Subsequent samples demonstrated weak reactions with the A cells and were noted to be resolved with 4C incubations. Weak reactivity with the A cells continued to be observed for the admission duration and was attributed to the patient’s disease state and treatment protocols. In November of 2022, the patient presented at a third OSH and typed as O positive by gel technology. In December 2022 the patient presented at our facility, was given a second round of chemotherapy and typed as A positive by solid phase. The patient was transfused 4 group A pRBC without issue. The patient returned back to the third OSH in March 2023 and typed as A positive by gel technology. This discordant typing led to collaboration with our blood bank as the patient was again being treated at our facility. Due to the unexplained change of blood type, sample was sent to a reference laboratory for DNA extraction and ABO sequencing (exon 6 and 7 and flanking intron regions).
Results/Findings: ABO sequencing results detected DNA polymorphisms c.261delG, c.297G, c.467T, c646A, c.771T, c.829A, and c.1061delC. The patient ABO genotype was reported to be A2.01/O.01.02 with a predicted ABO phenotype of Group A2. Conclusions: Serology will likely always remain the ABO testing method of choice for hospitals, but molecular testing for ABO sequencing proves to be invaluable for resolution of discordant serological ABO results. The patient’s clinical presentation may explain ABO discrepancies, but care must be taken to ensure the clinical presentation does not mask ABO subtypes.
Importance of research: Emphasizes the correlation between serological testing and molecular testing and the importance of using both when the situation calls for it. It also highlights that the most likely resolution for an ABO discrepancy should not be assumed and that follow up testing can be incredibly valuable.
