Syphilis Tests
Reviewed
Also called: rapid plasma reagin (RPR), Venereal Disease Research Laboratory (VDRL), fluorescent treponemal antibody absorption (FTA-ABS) test, agglutination assay (TP-PA), darkfield microscopy, Treponema pallidum particle agglutination assay (TP-PA)
Syphilis tests are used to screen for and diagnose syphilis, a sexually transmitted infection. Testing usually involves a screening blood test (RPR or VDRL) followed by a confirmatory blood test (FTA-ABS, TP-PA, etc.). If symptoms suggest brain or nervous system involvement, a cerebrospinal fluid test may be done. Screening tests look for antibodies that may be from syphilis; confirmatory tests look for antibodies specific to syphilis. A positive confirmatory test indicates a current or past syphilis infection. Treatment with antibiotics is effective, especially in early stages.
Specimen: Blood or cerebrospinal fluid (CSF)
Why this test may be ordered
- You have symptoms of syphilis (e.g., painless sore, rash, fever, swollen glands).
- Your sexual partner was recently diagnosed with syphilis.
- You are at high risk (multiple partners, unprotected sex, HIV, MSM, other STIs).
- You are pregnant (CDC recommends testing at first prenatal visit, and again at 28 weeks and delivery if at high risk).
Preparation and collection
You don't need any special preparations for a syphilis blood test. For a lumbar puncture, you may be asked to empty your bladder and bowels before the test.
Blood sample from a vein, or cerebrospinal fluid via lumbar puncture (spinal tap). At-home self-collection kits are available for screening only.
Blood test: There is very little risk. You may have slight pain or bruising at the needle site, but most symptoms go away quickly. Spinal tap: There is also very little risk. You may feel a pinch or pressure when the needle is inserted. After the test, you may have some pain or tenderness in your back, some bleeding at the insertion site, or a headache that may last for several hours to a week or more. Your provider may suggest treatment for the headache.
Understanding results
Syphilis testing usually involves two steps: a screening test (RPR or VDRL) and a confirmatory test (FTA-ABS, TP-PA, etc.). The screening test looks for antibodies that may be from syphilis. A positive screening result requires a confirmatory test. The confirmatory test looks for antibodies specific to syphilis. A positive confirmatory test indicates a current or past syphilis infection. The test cannot tell the difference between syphilis and related bacteria (yaws, bejel, pinta). Your healthcare provider will interpret your results and guide next steps.
- Screen-negative: You probably don't have a syphilis infection. Limitation: Antibodies may not be present yet if you were exposed very recently. Next step: If you think you were exposed, talk to your provider about whether you need another screening test.
- Screen-positive: You have antibodies that may be from a syphilis infection. Limitation: This is a screening result; other conditions can also cause a positive result. Next step: Your provider will order a second test to confirm whether or not you have syphilis.
- Confirmatory positive: Antibodies specific to syphilis were detected, indicating a current or past syphilis infection. Limitation: Cannot distinguish between a current infection and a past treated infection. Blood tests cannot distinguish syphilis from related infections (yaws, bejel, pinta). Next step: You will likely be treated with antibiotics. Treatment can cure early-stage syphilis but may not reverse late-stage damage. Repeat screening may be needed to monitor treatment.
- Confirmatory negative: No antibodies specific to syphilis were detected. You likely do not have a syphilis infection. Limitation: False negatives can occur if tested very early after exposure. Next step: Discuss any symptoms or concerns with your healthcare provider.
- Screening tests may be negative early after infection because antibodies take a few weeks to develop.
- A positive screening test does not confirm syphilis; a confirmatory test is required.
- Confirmatory blood tests cannot distinguish between a current and a past treated syphilis infection.
- Blood tests cannot tell the difference between syphilis and related infections (yaws, bejel, pinta).
- At-home kits are screening only; a confirmatory test is still needed.
What to do next
If you have a positive confirmatory test, you will likely be treated with antibiotics. You should inform any sexual partners so they can be tested. Repeat screening tests may be needed to monitor treatment effectiveness. Avoid sexual contact until treatment is complete.
- Do I need to be tested for syphilis?
- What do my results mean?
- Do I need a confirmatory test?
- What should I do if I have syphilis?
- How can I prevent spreading syphilis?