immunodiffusion assay reverse radial immunodiffusion assay 2013-11-13T15:02:47Z A technique used to determine the quantity of an antibody in a sample by measuring the diameters of circles of precipitin complexes surrounding a well in a gel such as agar in which the sample is placed. Antibody diffuses into a gel matrix containing a specific antigen and a ring of precipitate is formed, the diameter of which is directly proportional to the concentration of the antibody in the sample. Precipitin is an antibody that has specifically aggregated a macromolecular antigen to give a visible precipitate. JSmith MMO:0000440 measurement_method_ontology reversed single radial immunodiffusion test