VDRL / RPR (Syphilis Tests)
Definition
Syphilis tests detect antibodies that the immune system produces in response to the infection. Testing is done in two stages:
| Stage | Test | What it looks for |
|---|---|---|
| 1. Screening (non-treponemal) | RPR (Rapid Plasma Reagin) | A blood test that looks for an antibody called reagin |
| VDRL | Can be done on blood or cerebrospinal fluid; a broader range of antibodies | |
| 2. Confirmation (treponemal) | Treponemal tests | Antibodies specific to syphilis; distinguishes true infection from a false positive |
Purpose
For people with symptoms (rash, fever, sore throat, fatigue), those who have had contact with an infected partner, and those with risk factors (multiple partners, unprotected sex, HIV infection, other STIs). For pregnant women, testing is recommended at the first prenatal visit, again at week 28 and at delivery.
Results
- Negative screen, infection appears absent, but antibodies take weeks to develop (a false negative is possible early on)
- Positive screen, possible syphilis, but a confirmatory test is required
Risks and Limitations
The most important feature of this test:
Non-treponemal tests (RPR/VDRL) can give false positives due to autoimmune diseases and other infections; for this reason, a treponemal confirmatory test is required for an accurate diagnosis.
In other words, a positive screening result on its own does not mean "you have syphilis".