Treponema pallidum particle agglutination assay

The treponema pallidum particle agglutination assay (also called TPPA test) is an indirect agglutination assay used for detection and titration of antibodies against the causative agent of syphilis, Treponema pallidum subspecies pallidum.
In the test, gelatin particles are sensitized with T. pallidum antigen. Patient serum is mixed with the reagent containing the sensitized gelatin particles. The particles aggregate to form clumps when the patient serum is positive for syphilis. In other words, the patient's serum contains antibodies to T. pallidum. A negative test shows no clumping of gelatin particles. This is a type of specific treponemal test for syphilis.