The Rapid Plasma Reagin (RPR) test is one of the available screening tests for syphilis. The Venereal Disease Research Laboratory (VDRL) is another available screening test.
In the RPR, the laboratory will be testing the patient's serum for non specific antibody called reagin. Reagin antibodies are almost always produced by people with syphilis.
However, many infectious and non-infectious diseases and conditions can also form regain antibodies, these include: tuberculosis, malaria, measles, mononucleosis, and rheumatoid arthritis are just a handful of the diseases.
If a RPR or VDRL screening test comes up "positive" or "reactive", it must be confirmed with tests that test for the specific antibodies to the syphilis bacterium (Treponema pallidum).
The most common available treponemal antibody tests available are the fluorescent treponemal antibody absorption test (FTA-ABS) and Treponema pallidum particle agglutination assay (TPPA). So in a nutshell in one scenario, if a RPR is positive, but the FTA-ABS is negative, you are considered negative for syphilis.
Antibodies may not be able to be detected for up to three months after exposure to the bacteria, and the antibodies remain in the body for years. If you have had a past infection with syphilis and were treated, your test results could still be positive for years after treatment.
The labs will titer the blood for to determine the concentration of syphilis antibodies. The titer should be lower after successful treatment; if it remains the same or rises, you may have a persistent infection.
Why would my doctor order a RPR on me? If you are pregnant, you should be tested for antibodies to syphilis. Screening of all pregnant women is recommended by the US Preventive Services Task Force.
If the patient presents to their physician symptoms resembling syphilis or other sexually transmitted infection and depending on the state, the RPR test is required for applying for a marriage license.
What kind of sample is required? They will need a blood sample to test for either the RPR or VDRL.