Antibody of Undetermined Specificity - The Eyes Do Not See What the Mind Does Not Know: Are You Dealing with a Low Prevalence Red Blood Cell Antigens?

Abstract

For identification (ID) of irregular antibodies, a standard antibody identification (AI) panel consisting of 18 mandatory antigens expressed on reagent red blood cells is used. The phenotype for each antigen is listed on a red cell antigram provided with each lot of the ID panel. In addition, special type of low-incidence antigens that are clinically significant are separately mentioned on the left- or right-hand column or on the reverse of the antigram. These cases highlight the importance of diligent AI to ensure safe transfusions and prevent adverse transfusion reactions in patients. The ID of rare and low-incidence red cell alloantibodies is important in ensuring safe transfusions and preventing hemolytic disease of fetus and newborn. In routine practice, these types of antibodies are often categorized as having an undetermined specificity due to their rarity and low prevalence in the population. We describe two cases of successful ID of rare and low-incidence red cell alloantibodies, Anti-Colton-b (Co(b)) and Anti-Kpa. Type and screen and irregular AI were performed on Immucor NEO Iris® (SPRCA), for both the female patients. Autocontrol and direct agglutination test were performed by column agglutination technique method (BIO-RAD, Coombs Anti-Ig G cards) and were negative for both the patients. Analysis of respective antigrams was done to rule out or rule in irregular antibodies. Initially, the reaction pattern indicated the presence of anti-Co(b) and anti-Kpa. However, the reaction only occurred in one cell out of the 14 cells tested for both patients. To ensure accuracy, the samples were rerun using different lots using the SPRCA methodology. To confirm the presence of anti-Co(b) antibodies, a selected panel cell was treated with an enzyme to enhance the expression of the Co(b+) antigen. Anti-Co(b) and anti-Kpa alloantibodies were successfully identified and AHG crossmatched; compatible and phenotype-matched blood units were reserved for the patients. Low prevalence antibodies are often missed during antibody screening due to lack of corresponding antigen-positive cells in cell panels or due to their weak reaction pattern and considering it for nonspecific reaction.

Keywords

• alloantibodies
• antibody identification
• low-incidence antigens
• red cell antigram
• select cells