About the Immunodiffusion Test

Immunodiffusion is a qualitative or semi-quantitative test based on the principles of double diffusion described by Oudin and Ouchterlony. An antibody and its homologous soluble antigen are placed in separate wells cut in a suitable diffusion medium (agarose or CleargelTM) and allowed to diffuse outward into the medium. Between the two wells, a concentration gradient of each of the reaction components is established ranging from antigen excess closest to the antigen well, to antibody excess closest to the antibody well.  A visible line of precipitate forms at the point of equivalence.

Patient antibodies are tested for “identity” by placing patient serum adjacent to the wells of a known reference system. Additionally, the patient specimen is placed adjacent to a positive control to obtain maximum sensitivity (i.e. low-positive specimens will show a turning of the reference band when placed adjacently to a positive control). If an antigen-antibody complex is identical, a precipitin line forms an unbroken line of identity with the known reference system. The well patterns of the immunodiffusion plate are arranged to provide each patient test with a known reference system so that identity reactions are readily apparent (Figure 1). Partial identity and nonidentity reactions are also possible (Figure 1).

A partial identity reaction occurs when certain components of the antibodies are identical and others are not. Partial identity reactions indicate the simultaneous occurrence of both an identity reaction and a non-reaction. The “spur” represents the components that are unrelated. A nonidentity reaction will occur when the antigen-antibody complexes are different. The resulting “X,” or crossed reaction, indicates that two unrelated complexes are present.

Immunodiffusion Kits

Fungal Antigens, Positive Controls And Immunodiffusion Package Insert

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ID Plate Form

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