The "gold standard" diagnostic test for CWD is the Immunohistochemistry (IHC) test performed on the obex tissue of the brain (right) or specific lymphoid tissues.
IHC testing is a method utilizing antibody based staining which is evaluated using light microscopy. This test is both sensitive and specific. In addition, the microscopic methods used to detect positive staining also allow confirmation that the correct tissue and location within the tissue are present to detect the earliest accumulations of the prion agent. Other diagnostic tests utilizing enzyme-linked immunosorbent assay (ELISA) and other technologies that allow more rapid testing of larger numbers of samples have been, and continue to be, developed. Several test kits using ELISA and other technologies have been licensed by USDA's Center for Veterinary Biologics for CWD diagnosis in wild elk and deer. CWD testing can only be performed by approved laboratories that are part of the USDA's National Animal Health Laboratory Network system. A rectal associated mucosal lymphoid tissue (RAMALT) biopsy (live-animal) test has been developed by researchers and appears to hold promise for future use in certain CWD monitoring or management situations in farmed cervids. This technique utilizes the current IHC testing technologies described above.
Information on brain (obex) and lymphoid tissue sample collection is found in the APHIS CWD Sample Collection Guidance .