👉 Agglutination of red blood cells resulting in the formation of small clumps visible to the naked eye.
◈ There are 3 kinds of hemagglutination reactions:
- In the first, used for the determination of blood groups, specific antibodies are made to act on the surface antigens of the red blood cells.
- The second kind is represented by passive hemagglutination reactions. Here, the red blood cells play a role of inert support on which soluble antigens are artificially fixed; they will be agglutinated by specific antibodies, a reaction applied in the TPHA (Treponema Pallidum Hemagglutination Assay).
- The third type used in virology. Some viral proteins, hemagglutinin, are able to bind to surface receptors in red blood cells. Thus, the attachment of a virion to two neighboring red blood cells leads to their agglutination.
◈ A positive reaction is manifested by the formation of a haze on the surface while the appearance of a pimple at the bottom of the cup is an indicator of a negative reaction.