What Does RPR Mean on a Blood Test?

What it means

RPR is a non-treponemal test for syphilis, meaning it does not detect the syphilis germ directly. It finds antibodies, once called reagins, that the body makes when syphilis is active and damaging cells. The test uses tiny charcoal particles that clump together when these antibodies are present, which makes the result easy to see.

Clinics use RPR in two ways. For screening, a reactive RPR is followed by a treponemal test, which looks for antibodies aimed at the syphilis germ itself, to confirm infection. For follow-up, the RPR is reported as a titre, such as 1:4 or 1:64, which shows how strongly the sample reacts. After treatment, the titre is expected to fall over the following months, so doctors repeat it to check progress. Some labs now do the treponemal test first and use RPR second; this is called reverse screening.

RPR is closely related to VDRL. Both look for the same kind of antibody, but they are different methods, so it is best to follow the same test at the same lab over time.

Where you may see it

• Sexual health clinic results, often with a treponemal test such as TPPA or a syphilis EIA
• Pregnancy screening results
• Follow-up blood tests months after syphilis treatment
• HIV clinic routine screening results