Rapid Plasma Reagin (RPR), Serum

Medical Test

Treponema pallidum, the etiological agent of syphilis, induces the production of at least two types of antibodies in human infection: anti-treponemal antibodies that can be detected by fluorescence treponemal antigen assay (FTA-ABS), and anti-nontreponemal antibodies (reagin) that can be detected by RPR antigen. RPR is a latex flocculation based test that uses a cardiolipin-lecithin-cholesterol carbon-containing antigen reagent. If antibodies are present, black carbon clumps are produced by flocculation indicating a positive test for RPR. It is a rapid test used as a screening test and in suspected primary and secondary syphilis. It is not specific for syphilis and false positives can occur with disorders such as malaria, systemic lupus erythematosus, infectious mononucleosis, viral pneumonia as well as the status of being pregnant.  Positive results must be confirmed by IFA antibody testing or by PCR. The test is also used for treatment monitoring and disease management. After treatment with antibiotics, the levels of syphilis antibodies should fall. These levels can be monitored with the RPR titer.  Successful therapy is indicated by a 4 fold decrease in titer within 6 months after initiation of therapy for primary and secondary stages.  Unchanged or rising levels can mean a persistent infection.