Syphilis is a complex, multistage disease caused by Treponema pallidum. When left untreated, syphilis can result in severe cardiovascular, ocular and neurological complications. Infectious syphilis is also associated with an increased risk of HIV transmission.

Serologic testing to diagnose syphilis includes the use of both nontreponemal and treponemal tests. Initial screening is usually carried out using a treponemal test with confirmation using a non-treponemal option such as the rapid plasma reagin (RPR) test. RPR usually become positive approximately 10-15 days after the appearance of the primary chancre (i.e. around 6 weeks after infection). RPR titres correlate grossly with disease activity and are used to monitor both disease activity and efficacy of treatment.