A case report of soluble A antigen confounding the blood type in a haplo-identical hematopoietic stem cell transplant patient with graft-versus-host disease.

BACKGROUND

ABO-incompatible (ABOi) hematopoietic stem cell transplantation (HSCT) is often associated with ABO discrepancies post-HSCT. Re-emergence of the patient's original type post-HSCT may signal graft loss, disease relapse, recent transfusion, or soluble ABO antigen. We present a group A pediatric patient with leukemia who underwent a minor ABOi HSCT from a group O donor with persistent and increasing A reactivity 2 years post-HSCT.

METHODS

The patient's electronic medical and laboratory records were reviewed. ABO, Lewis typing, and direct antiglobulin (DAT) tests were performed by column agglutination and/or tube method. Soluble anti-A was demonstrated by adsorption and human anti-A neutralization. Elution of soluble A antigen was performed by incubation of patient red cells with group A1, Le(a + b-) plasma.

RESULTS

The patient typed as Le(a-b+) and demonstrated 1+ reactivity with anti-A reagent, which increased (4+) during an episode of gastrointestinal graft-versus-host disease (GVHD). There was no evidence of disease relapse with 100% donor cells by molecular testing, normal blood counts, and a negative DAT. A high level of soluble A-antigen in patient plasma was demonstrated by adsorption and anti-A neutralization studies. Finally, soluble A antigen was successfully eluted from patient RBCs to reveal only group O donor type RBCs.

DISCUSSION: We present a case of persistent A antigen post-ABOi HSCT due to soluble A antigen of patient origin. Soluble A antigen was demonstrated using adsorption, neutralization studies, and a modified elution method previously described for Lewis antigens. This case suggests increased soluble ABO antigen in the setting of gut GVHD.