Treponema pallidum hemagglutination assay (TPHA) test
Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
The Syphilis TPHA test is a classic, indirect hemagglutination test used for the detection and titration of antibodies against the causative agent of syphilis,Treponema pallidum.
In the test red blood cells (erythrocytes) are sensitized with antigens from T. pallidum. The erythrocytes will then aggregate together to form distinctive patterns on the surface of a microplate wells when exposed to syphilitic serum.
False Positives are common in this test. This is typically caused by antibodies directed against other non-pathogenic or non target treponemas, such as T. pallidum subsp endemicum, T. pallidum subsp pertenue, and T. carateum. These antibodies can be adsorbed out of the test sample by a variety of methods thereby reducing false positives for syphilis.