AGID blood test for Johne’s disease

A simple two-day test to confirm a diagnosis of Johne's disease in cattle is the AGID (agar-gel immunodiffusion) test. Serum from the animal is place in one well, a positive control is place in another, and soluble antigen is place in the third (top well). Formation of a white line of precipitation between the sample well and the antigen well (arrow) is considered a positive test. This test is commercially available (Rapid Johne's Test, ImmuCell Corp.) and can be done without need of special equipment. It also works well in small ruminants, however, the exact accuracy of the test has not been reported.