How radial immunodiffusion differs from immunodiffusion?

Radial immunodiffusion (RID) is a specific type of immunodiffusion where an antigen is allowed to diffuse radially from a well in a gel containing antibodies, forming a gradient that leads to the formation of a precipitation ring. In contrast, immunodiffusion generally refers to any method where antigens and antibodies diffuse in a medium to form visible precipitates, which may not necessarily be radial. RID quantifies the antigen concentration based on the diameter of the precipitation ring, while other forms of immunodiffusion may not provide quantitative results. Overall, RID is a more standardized and quantitative approach compared to general immunodiffusion techniques.