In reverse passive agglutination, which component is covalently bound to the carrier particle?

• A. Antigen
• B. Antibody
• C. Complement
• D. Lipid

Answer: (A)

In reverse passive agglutination, the carrier particle is prepared by covalently binding antibody molecules to its surface. The idea is that the antibody on the carrier will recognize and bind the antigen that is present in the patient’s sample. When many carrier particles, each bearing antibodies, encounter the target antigen, cross-linking occurs through the antigen linking multiple particles together, producing visible agglutination. This arrangement allows detection of the antigen without needing antibodies from the patient serum. If the antigen were bound to the carrier instead, you’d be describing standard passive agglutination rather than the reverse setup. Covalent attachment of the antibody to the carrier ensures stable, oriented binding sites for the antigen and reliable agglutination signals.