Immunodiffusion is a laboratory testing technique people can use to check for the presence of antibodies in a sample and determine their concentrations. In this test, a technician adds antibodies and antigens separately to a plate filled with a semisolid medium like agar gel. The plate is left alone to mature, and as the antigens and antibodies diffuse through the medium, they bind to each other and create visible precipitates the technician can see on the surface of the material. These can be used to confirm the presence of a given antibody and to determine the concentration present in the sample used for the test.
Several different immunodiffusion techniques are used in labs, including radial and Ouchterlony double immunodiffusion. Sample materials can include slurries of human cells, tissue scrapings, and other materials. In some tests, multiple holes are created in the medium and filled with different antigens to check for an array of responses. If the sample contains an antibody to one of the antigens placed in the gel, it will react, creating a line or ring, depending on the sample and the type of test.
This is one among an assortment of immunology lab tests people can use to collect information about a sample with unknown properties. If antibodies are present, it indicates the sample comes from a person either actively fighting an infection, or with a history of exposure to a given antigen. The concentration can provide information about the timing of the exposure. It usually takes at least 24 hours for the plate to mature so the technician can take a reading. There is also a risk of a false negative if there is a problem with the sample or the antigens the technician uses in the test.
A doctor can request an immunodiffusion test to collect information about a patient, or this testing may be part of scientific research. The antibodies and antigens do not need to be human in origin; the same testing can be used for animals as well. In the test results, the technician will discuss the materials used, whether a response occurred, and the intensity of the response. This information can be used to move forward with diagnosis or treatment of the patient.
The tests available at a given lab vary. Most labs publish catalogs with information about their testing capacity and pricing so people can decide where to send samples for testing. Labs offering immunodiffusion testing may not offer all types, and this could be important for a doctor or researcher to know about.