flocculation reaction

floc·cu·la·tion re·ac·tion

a form of precipitin reaction in which precipitation occurs over a narrow range of antigen:antibody ratio, owing chiefly to peculiarities of the antibody (precipitin).
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3) The prozone phenomenon is a false-negative reaction to a serologic test that occurs when very high antibody titers in the serum prevent the formation of the antibody-antigen lattice needed to visualize a flocculation reaction.
When serum from a syphilis-infected individual is added to a suspension of cardiolipin antigen and charcoal, an antibody-antigen lattice forms, with the flocculation reaction visualized as clumping of the charcoal.
The prozone effect in syphilis testing refers to a false negative result seen in cases of high titers of antibodies interfering with the proper formation of the antigen-antibody lattice network needed to visualize a positive flocculation reaction.