The technique of reversed passive latex agglutination (RPLA) enables soluble antigen such as bacterial toxins to be detected in an agglutination assay. In a standard agglutination assay, soluble antibody reacts with particulate antigen such as bacterial cells. However, in a reversed agglutination assay the antibody, which is attached to particles, reacts with the soluble antigen. The particles (in this case, latex) do not themselves play a part in the reaction and they are therefore passive.

• The cross-linking of the latex particles by the specific antigen/antibody reaction results in the visible latex agglutination reaction