Which antibody is associated with mixed-field agglutination?

• A. anti-Le^a
• B. anti-K
• C. anti-D
• D. anti-Lu^a

Answer: (D)

The pattern you’re looking for appears when two distinct red cell populations are present in the same sample, so some cells clump while others do not in the antibody’s presence. Anti-Lu^a binds specifically to the Lu^a antigen, which is not expressed on all red cells. In a mixed population—some cells expressing Lu^a and others not—the antibody will cause agglutination of the Lu^a-positive cells while Lu^a-negative cells remain unagglutinated, giving the characteristic mixed-field appearance. The other antibodies target antigens that are more uniformly expressed across most cells, so they don’t typically produce mixed-field patterns in routine testing. Thus, anti-Lu^a is the one most associated with mixed-field agglutination.