Which crossmatch procedure is used to detect antibodies that react at the antiglobulin phase?

• A. Immediate spin crossmatch
• B. Donor antibody screen
• C. AHG crossmatch
• D. Type & Screen

Answer: (C)

Antibodies that react at the antiglobulin phase are typically IgG antibodies that do not cause visible agglutination at immediate spin. The AHG crossmatch uses antihuman globulin reagent to detect antibodies that have bound to donor red cells and are only revealed after incubation and the antiglobulin step. In this procedure, donor cells are mixed with the recipient’s plasma, incubated (often at 37°C), and then AHG is added to reveal any sensitization as agglutination. This ensures detection of clinically significant antibodies that react at the antiglobulin phase, which is why this crossmatch is used for antibodies reacting at that phase. Immediate spin crossmatch detects reagents that react at room temperature and is not sensitive to these IgG antibodies; the donor antibody screen and Type & Screen are screening or typing steps, not crossmatch procedures designed to detect antiglobulin-phase reactions.