Technical Specialist II Johns Hopkins Hospital Baltimore, Maryland, United States
Background/Case Studies: Background/Case Study: A 61 year old male was admitted for surgical resection of rectal cancer. The patient’s ABORh front type was AB positive; however, there was unexpected reactivity with reagent B red blood cells (RBC) in the reverse type on multiple specimens. Acquired B phenomenon was suspected, but ABO genotyping identified A1 and B alleles (predicted A1B phenotype). High-resolution testing was unavailable to assess B allele variants. The unexpected reactivity was determined to be anti-IB with an underlying anti-I reactive only at 4°C.
Study
Design/Methods: Study
Design/Methods: ABORh typing was performed by commercial monoclonal anti-A, anti-B, and anti-D antisera and commercial A1 and B RBC at immediate spin (IS). The antibody detection test was performed by solid phase red cell adherence. Additional testing was performed using commercial reagent RBC, volunteer donor RBC, and cord RBC at IS, room temperature (RT) and 4°C incubation. Adsorption studies were performed using ficin treated type O and B RBC incubated for 30 minutes at 4°C. Titrations were performed using type O and B RBC at RT and 4°C phases. A1 typing was performed with commercial anti-A1 lectin. ABO genotyping was performed at an outside laboratory.
Results/Findings: Results/Findings: The patient’s front type was AB pos: anti-A(4+), anti-B(4+) and anti-D(4+). Patient RBC reacted 3-4+ with type A patient plasma and commercial anti-A1 lectin. The monoclonal control and antibody detection tests were negative. The patient’s plasma was reactive at IS and RT with B and A2B RBC, but not with A1, A1B, or O RBC. Reactivity was noted at 4°C incubation with autologous, B, and A2B RBC (3-4+), and O and A1B RBC(1+-2+). Type B, O, and A2B cord RBC were negative at IS; however, the B cord specimen and one of the O cord specimens reacted weakly at 4°C. The patient’s plasma adsorbed with O RBC showed reactivity with B cells at 4°C, while adsorption with B RBC removed all reactivity. Titration with B and O RBC at 4°C had results of 4 and 1, respectively. Conclusions:
Conclusion: Acquired B phenomenon was ruled out with genetic testing. Possible B variants could not be excluded, but would be unlikely with a 4+ anti-B reaction. The antibody showed strongest reactivity at IS with B and A2B adult RBC, and negative reactions with cord RBC, suggesting that the antibody has a combined B and I antigen specificity. Negative reactivity with A1B RBC may be explained by weaker expression of B antigen on A1B RBC compared to A2B RBC. Reactivity at 4°C with O and A1B RBC was attributed to anti-I. There are other rare reports of anti-IB in type B and A1B patients. Anti-IB is likely an autoantibody and is not expected to cause hemolytic transfusion reactions. An “O” RBC transfusion requirement was initiated, but the patient did not require transfusion. The anti-IB was no longer detected 3 months post-operatively.
Importance of research: ABO genotyping is a useful tool to solve ABORh discrepancies, especially in cases where acquired B is suspected due to an AB front type with unexpected anti-B in the plasma. While anti-IH is commonly encountered, it is unusual to encounter compound anti-IB specificity. This case highlights the use of genotyping and advanced serologic methods to investigate an anti-IB causing an ABORh discrepancy.
