RPR

RPR is the acronym for "Rapid Plasma Reagin" and refers to a blood test for screening for syphilis.

The RPR test detects non-specific antibodies that the body forms in response to a syphilis infection. It is a non-treponemal test and does not look directly for the pathogen, but for antibodies produced by the infection. Areas of application:

• Routine STI screening
• Examination during pregnancy (prevention of congenital syphilis)
• Monitoring the success of treatment after a confirmed diagnosis

Procedure:

• Blood sample taken from a vein; result usually within 1-2 days.

The RPR test as well as the VDRL test are used as non-treponemal serological tests to screen for active syphilis infections and to monitor the response to treatment. Due to their lack of specificity, positive results should be confirmed by treponema-specific tests, such as the fluorescent treponema antibody absorption test(FTA), the T. pallidum enzyme immunoassay (TP-EIA), the T. pallidum particle agglutination test (TPPA) and the chemiluminescence automated immunoassay (CLIA) (Lum B et al.2025).

Results:

• Reactive (positive): Suspected syphilis. A treponemal test (e.g. TP-PA or FTA-ABS) is always required to confirm the diagnosis.
• Non-reactive (negative): Indicates no infection, but can be false-negative in very early or late stages.
• False-positive results are possible. A confirmatory and follow-up test is therefore always necessary.

Reasons for a false-positive result

• Pregnancy
• Autoimmune diseases (e.g. systemic lupus erythematosus)
• Other infections (e.g. malaria, certain pneumonia)

Reasons for a false negative result:

• Prozone phenomenon

1. Awake P et al.(2022) Prozone phenomenon in secondary syphilis with HIV co-infection: Two cases. Indian J Sex Transm Dis AIDS 43:183-185
2. Cebolla-Verdugo M et al. (2025) Syphilis in people living with HIV: Diagnostic challenges. J Dtsch Dermatol Ges 23: 887-888.
3. Janier M et al. (2021) 2020 European guideline on the management of syphilis. J Eur Acad Dermatol Venereol 35:574-588.
4. Lum B et al.(2025) Rapid Plasma Reagin. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. PMID: 32491664.
5. Smith G et al. (2004) The prozone phenomenon with syphilis and HIV-1 co-infection. South Med J 97:379-382.
6. Spangler AS et al. (1964) Syphilis with a negative blood test reaction. JAMA 189:87-90.