The TPHA test is an indirect hemagglutination assay used for the detection and titration of antibodies against the causative agent of syphilis, Treponema pallidum. Syphilis is a sexually transmitted disease that occurs throughout the world and its incidence seems to be slightly on the increase at this time. Classically, the disease involves three different phases. The primary phase is characterized by a painless lesion called a chancre. This primary lesion spontaneously resolves and a secondary phase follows which involves the development of mucocutaneous lesions all over the body. After a subsequent asymptomatic latent period which can last several years, final stage or tertiary syphilis develops. The infection spreads systemically and internal lesions can cause cardiovascular, mucocutaneous (especially affecting the gums) and neurological (general paresis and tabes dorsalis) symptoms. This test is highly sensitive and specific test for the serologic diagnosis of syphilis. A POSITIVE result indicates past or current infection with Treponema pallidum. See Rapid Plasma Reagin (RPR) Test, Serum