Rapid plasma reagin

Rapid Plasma Reagin (RPR) refers to a type of test that looks for non-specific antibodies in the blood of the patient that may indicate that the organism (Treponema pallidum) that causes syphilis is present. The term "reagin" means that this test does not look for antibodies against the actual bacterium, but rather for antibodies against substances released by cells when they are damaged by T. pallidum.
In addition to screening for syphilis, an RPR level (also called a "titer") can be used to track the progress of the disease over time and its response to therapy.