Which antibody will usually be detected in the antiglobulin phase of a crossmatch?

• A. anti-D
• B. anti-Jk^a
• C. anti-K
• D. anti-Fya

Answer: (B)

The antiglobulin phase of a crossmatch is designed to reveal IgG antibodies to non-ABO red cell antigens that do not cause visible agglutination at the immediate spin. These antibodies bind to donor red cells and are only detected after adding antiglobulin, which bridges the cells and produces a visible reaction.

Anti-Jk^a fits this pattern well. JK^a is a fairly common red cell antigen, and many transfusion patients become alloimmunized to it. The antibodies against JK^a are typically IgG and react at body temperature, so they are detected in the AHG phase rather than at immediate spin. While antibodies to other antigens like Kell or Fy^a can also be encountered, anti-Jk^a is one of the most commonly seen in this phase of crossmatching.

Anti-D can be present if someone has been sensitized, but it is not the antibody most routinely detected in the AHG crossmatch across typical practice; the crossmatch more frequently reveals non-ABO antibodies like anti-Jk^a.