RPR (Rapid Plasma Reagin)

Useful For


Confirmation of REACTIVE Syphilis TP test and used as a quantitative nontreponamal test to establish a baseline titer and to monitor treatment response.


Indications for Testing


Establishing baseline titer and follow-up monitoring of treatment response.


Infants (born to mothers with reactive syphilis serology)


See Special Instructions (Congenital Syphilis)


Special Instructions and Forms




Clinical Information


The serological diagnosis of syphilis is divided into treponemal tests for measuring syphilis antibodies and nontreponemal tests. Nontreponemal tests, such as the rapid plasma reagen (RPR) test and the veneral disease research labortaory (VDRL) test, detect reagin-based antibodies produced in response to treponemal infection. Reagin is a lipoidal antigen. The test lacks specificity because reactive antibodies can be elicited in diseases and conditions unrelated to syphilis, giving rise to biological false-positives. However, nontreponal tests are useful for determining the stage of infection and to monitor treatment success. Successful treatment reduces the amount of lipoidal antigen that can be monitored by observing a decrease in RPR/VDRL titre.


Nontreponemal tests (RPR and VDRL) measure IgM and IgG antibodies to cardiolipin and other lipids released from damaged host cells or from treponemes. Nontreponemal tests become positive one to four weeks after the appearance of the primary chancre, and six weeks after exposure. Quantitative titer values monitor the course of disease during and after treatment, detects relapse, and can also serve to detect reinfection.


Reference Values






REACTIVE: #value titer


NONREACTIVE: (negative)


– Sequential serologic tests in individual patients should be performed using the same testing method (e.g. VDRL or RPR), preferably by the same laboratory.


– A fourfold change in RPR titer (e.g. from 1:16 to 1:4 or from 1:8 to 1:32), is considered necessary to demonstrate a clinically significant difference between two test results.


– Serological tests for syphilis are uniformly reactive with yaws, pinta, and nonvenereal endemic syphilis (bejel). Therefore, patient history, the clinical appearance and anatomic locations of the lesions, the mode of transmission, and the age of the individual are the only criteria that can be used to diagnose these infections as separate entities.


Primary and secondary syphilis follow-up


– RPR should be performed 6 and 12 months after treatment (3, 6, 9, 12, and 24 for HIV-infected); more frequent evaluations might be prudent if follow-up is uncertain.


– For most HIV-infected persons, serologic tests are accurate and reliable for the diagnosis of syphilis and for following a patient’s response to treatment. However, atypical syphilis serologic test results (i.e. unusually high, unusually low, of fluctuating titers) can occur in HIV-infected persons.


– Patients who have a sustained fourfold increase in RPR titer (i.e., compared with the maximum or baseline titer at the time of treatment) probably failed treatment or were reinfected. Additional RPR testing should be submitted to confirm. Because treatment failure cannot reliably be distinguished from reinfection, a CSF analysis may be indicated.


– Persons who’s titers do not decline should be reevaluated for HIV infection


Latent syphilis


– Early latent syphilis cannot reliably be distinguished from late latent syphilis solely on the basis of nontreponemal titer.


– Quantitative nontreponemal serologic tests should be repeated at 6, 12, and 24 months after treatment, with HIV-infected individuals requiring an 18 months repeat as well. If during 12 – 24 months the RPR titer does not decline fourfold CSF examination may be indicated.


Tertiary syphilis


Limited information available on follow-up of patients who have tertiary syphilis.




Follow-up CSF examinations may be can be used to evaluate changes in CSF-VDRL after therapy; however changes in CSF-VDRL occur more slowly than cell counts.




Serologic titers should be repeated at 28-32 weeks’ gestation and at delivery as recommended for the stage of the disease. RPR can be repeated monthly in woman at high risk of reinfection.


Infants and children


All seroreactive infants (or infants whose mothers were seroreactive at delivery) should receive RPR testing every 2-3 months until the test becomes nonreactive, or the titer has decreased fourfold. RPR titers should decline by age 3 months and should be nonreactive by age 6 months if the infant is not infected. If RPR titers are stable or increase after age 6-12 months, the child should be reevaluated.


Clinical Reference


Ratnam, S. Canadian STI Best Practice Laboratory Guidelines: The laboratory diagnosis of syphilis. Can J Infect Dis Med Microbiol 2005;16(1):45-51.


Centers for Disease Control and Prevention. Sexually transmitted diseases treatment guidelines. MMWR 2010;59(No. RR-12):1-110.


Tsang, R.S.W., S.M. Radons, M. Morshed and the Syphilis Laboratory Task Group of the Canadian Public Health Laboratory Network. Laboratory diagnosis of syphilis: A survey to examine the range of tests used in Canada. Can J Infect Dis Med Microbiol 2011;22(3):83-87.


Sena, A. C, L. W. White, and P. F. Sparling. Novel Treponema pallidum serologic tests: A paradigm shift in syphilis screening for the 21st century. Clin Infect Dis 2010;51(6):700-708.


Canadian Pediatric Society. Congenital syphilis: no longer just of historical interest. Paediatr Child Health 2009;14(6):1-5.


Abbott. 2009. ARCHITECT System Syphilis TP: package insert. Abbott Diagnostics Division, Wiesbaden, Germany.


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