| ID | Immunodiffusion | (ID), also called Double diffusion (DD) or the Ouchterlony technique, is the classical procedure used to detect the presence of antibodies and determine their specificity by visualization of "lines of identity" (precipitin lines). These precipitin lines (precipitated antigen-antibody complexes) form where the binding concentrations of antigen and antibody are equivalent. Patient serum diffuses from one well through the gel and reacts with a known specific antigen (or antibody) which diffuses through the gel from a second well. DD is strictly qualitative, although the density of the precipitin line and the distance of the line from the sample well may give some indication of the antibody concentration. |