A latex fixation test (or latex agglutination test) is an agglutination technique used to detect antigens, such as those produced in response to the rubella virus or the rheumatoid factor. May be used for Rickettsia, coccidioidomycosis, though numerous sources of interferences (e.g., large immune complexes and high protein concentrations) lessen the utility of the latex agglutination (LA) test in most situations. There is an excellent LA test for cryptococcus. It also is used in definitive diagnosis of Group A streptococcus.
In a latex fixation test, a sample is mixed with latex beads coated with antibodies. If the antigen is present, it will react with the antibodies causing the latex beads to clump.