Which test is used to determine the antibody specificity by testing patient plasma against a panel of cells with known antigen profiles?

• A. Direct antiglobulin test
• B. Flow cytometry crossmatch
• C. Selected cell panel
• D. Antibody titration

Answer: (C)

Finding out which antigen an antibody targets is done by testing the patient's plasma against a panel of red cells with known antigen profiles. The selected cell panel is a curated set where each cell has a defined combination of antigens. If the patient’s plasma contains an antibody against a specific antigen, it will react with all cells expressing that antigen and not with cells lacking it, producing a pattern that reveals the antibody’s identity. This approach is different from the direct antiglobulin test, which looks for antibodies coated on a person’s own red cells rather than identifying the antibody’s target. It also differs from flow cytometry crossmatching, which assesses overall compatibility and can detect antibodies but is not primarily used to define antibody specificity from a panel of antigens. Antibody titration measures how strong the antibody reaction is by serial dilutions, not which antigen is targeted.