Hemagglutination refers to a form of agglutination that involves which cells?

• A. lysing of bacteria
• B. specific form of agglutination that involves red blood cells
• C. agglutination of latex beads
• D. precipitation of soluble antigen

Answer: (B)

Hemagglutination is the clumping of red blood cells caused by cross-linking between RBC surface antigens and antibodies or viral proteins that bind to those antigens. In this kind of reaction, the particles being clumped are the red blood cells themselves, which is why the term specifically refers to hemagglutination. This is the basis for blood typing, where antibodies against A or B antigens cause RBCs with those antigens to agglutinate, producing a visible positive reaction. It differs from lysing bacteria (which would break open cells), from latex bead agglutination (where the particles are inert beads, not cells), and from soluble antigen precipitation (where dissolved molecules come out of solution rather than cross-linking cells).