Transfusion Medicine Division, The Johns Hopkins Hospital Baltimore, Maryland, United States
Background/Case Studies: A 62-year-old White female, without known antibodies, was transfused two units of red blood cells (RBCs) for symptomatic anemia and gastrointestinal bleeding. Ten days later, the patient presented with a positive antibody detection test (ADT). Antibody identification (ABID) revealed an apparent antibody to an antigen of high prevalence (AHP). Further investigation demonstrated an underlying alloantibody which caused confounding results in the initial serologic identification.
Study
Design/Methods: ABID was performed by Immucor solid phase red cell adherence (SPRCA) and Ortho Diagnostics column agglutination test (CAT). Reagent RBC were treated with 0.2M dithiothreitol (DTT) and tested by LISS tube method. Ficin treated RBC were tested by CAT. Serologic phenotyping for common antigens was performed using commercial monoclonal antisera. Frozen RBC of Yt(a-) phenotype and sera known to contain antibodies to AHP were obtained from an internal collection of rare sera/cells and tested by CAT. Yt antigen genotyping was performed by an outside laboratory by multiplex PCR with DNA microarray hybridization.
Results/Findings: ABID panels showed reactivity with all reagent RBC. Variable reactivity was noted on SPRCA (weak-4+) while CAT panels showed 2+ reagent RBC reactivity. DTT and ficin treated RBC were positive (1+-2+). The patient’s phenotype was C-c+E-e+; K-; Fy(a+b+); Jk(a-b+); M+N-S+s+. Review of the variable reactivity on the SPRCA panel and serologic phenotype revealed a probable anti-Jka alloantibody in addition to the antibody to an AHP. Because the initial DTT treated RBC from the ADT were Jk(a+), additional DTT treated RBC of Jk(a-) phenotype were tested and found to be negative. Jk(a-) ficin treated RBC remained positive. The patient was phenotyped for AHP known to be DTT sensitive, ficin positive/variable, and found to be Kn(a+), McC(a+), Lu(b+), Cr(a+), Hy+, Yt(a-b+). The patient’s plasma was negative with two sources of Yt(a-) RBC, identifying anti-Yta specificity. Genotyping confirmed the patient to be Yt(a-b+). Conclusions: Unexpected results caused by underlying antibodies can interfere with the investigation of antibodies to an AHP. Anti-Yta antibodies are considered ficin sensitive but may show variable reactivity. In our case, due to the interfering anti-Jka, the initial serologic results suggested the antibody was directed against an AHP that was ficin and DTT resistant, which is not characteristic of antibodies in the Yt blood group system. Identification of the underlying anti-Jka and retesting Jk(a-) DTT treated RBC assisted in the identification of anti-Yta. Thorough investigations are needed for antibodies directed against AHP and often require multiple testing methods and knowledge of the expected serologic reactions of blood group antigens.
