The rapid plasma reagin (RPR) test has several useful purposes. It is used to screen asymptomatic individuals for syphilis, diagnose symptomatic infection, and monitor disease activity and response to treatment. Unlike the fluorescent treponemal antibody absorption (FTA-ABS) test, which measures specific antibodies to the syphilis bacterium, the RPR test measures nonspecific antibodies that are produced when Treponema pallidum interacts with human tissue. These antibodies also cross-react with a purified mixture of lipids (cardiolipin, lecithin, and cholesterol), known as "reagin," which is used as the substrate in the RPR test.
The RPR is a simplified version of the other nonspecific screening test for syphilis, the VDRL test. The RPR card test uses a mixture of reagin and carbon particles to which a patient's serum is added. Flocculation, or clumping, of the particles is read as a "reactive" or positive test. The test can be quantitated by examining serial dilutions of serum. A difference of two dilutions is required to demonstrate a significant difference between two tests.
Judith E. Wolf
(see also: Antibody, Antigen; Fluorescent Treponemal Antibody Absorption; Syphilis; VDRL Test )
Hook, E., and Marra, C. (1992). "Acquired Syphilis in Adults." New England Journal of Medicine 326:1060–1069.
Wolf, J. (1997). "Syphilis." In Current Diagnosis, 9th edition, eds. R. Conn, W. Borer, and J. Snyder. Philadelphia, PA: W. B. Saunders.