Syphilis Test: Blood Tests, RPR and What Results Mean

Syphilis can be quiet for a long time, and untreated it can cause serious problems. It is also curable with antibiotics from a clinician, which makes testing worthwhile. Here is how the tests work and how to read the results.

How is syphilis tested?

The CDC says that most of the time, healthcare providers use a blood test. If there is a sore, some providers test fluid from the sore instead. MedlinePlus says a syphilis test is a blood draw from a vein in your arm, and no special preparation is needed.

Syphilis testing normally takes two steps, because one test alone is not enough. The CDC says a presumptive diagnosis requires two laboratory serologic tests, one nontreponemal and one treponemal.

What is the difference between RPR, VDRL and treponemal tests?

• Nontreponemal tests (RPR and VDRL). MedlinePlus says RPR looks for an antibody called reagin, and that screening antibodies can come from some autoimmune diseases and other infections. The CDC says VDRL and RPR are equally valid.
• Treponemal tests. These look for antibodies made specifically against the syphilis bacteria. They are used to confirm a first result.

Some labs reverse the order and screen with an automated treponemal test first. The CDC calls this the reverse sequence algorithm. Either way, a second kind of test follows to confirm.

What do syphilis test results mean?

• Negative screening test. MedlinePlus says a negative screening result means you probably do not have syphilis. If you were exposed recently, you may need another screening test.
• Screening positive, confirmation positive. This points to syphilis, and a clinician will talk through treatment.
• Screening positive, confirmation negative. This may be a false positive on the first test.

Treponemal tests usually stay reactive for life, according to the CDC, even after successful treatment. Ask your clinician which test your result came from and what it means for you.

Can a syphilis test be a false positive?

Yes, which is why confirmation matters. The CDC says false-positive nontreponemal results can be linked to conditions including other infections such as HIV, autoimmune conditions, vaccinations, injecting drug use, pregnancy and older age. A second, treponemal test helps sort this out.

How soon after exposure can a syphilis test detect it?

The CDC does not state a window period. MedlinePlus says antibodies can take a couple of weeks to develop, and a negative screening test may need repeating if you were exposed recently. STDCheck’s page says to wait a minimum of 3 to 6 weeks after exposure before testing. Use the longer number if you want to be cautious.

If you have a sore, don’t wait. A clinician can test fluid from the sore. The CDC says darkfield examination and molecular tests of sore fluid are definitive methods for diagnosing early syphilis, and that no T. pallidum direct-detection molecular NAATs are commercially available, so ask what the clinic can do.

Who should be tested for syphilis?

The CDC recommends at least annual syphilis screening for sexually active men who have sex with men, and every 3 to 6 months if they are at increased risk. It recommends screening at the first HIV evaluation and at least annually after that for sexually active people with HIV, and screening of adults at increased risk. Pregnant people have their own schedule: see below.

Is syphilis testing different in pregnancy?

Yes. The CDC says all pregnant women should receive syphilis testing at their first prenatal visit, and should be retested at 28 weeks and at delivery if they are at increased risk. Syphilis can pass to a baby, and the CDC says these babies can have serious health problems, which is why testing and early treatment matter.

What happens after a positive result?

The CDC says syphilis is curable with the right antibiotics from your healthcare provider, although treatment might not undo any damage the infection can cause. Having syphilis once does not protect you from getting it again. The NHS says people return several times in the first 12 months after starting treatment to be retested.

Can I get a syphilis test online or at home?

The CDC says FDA-approved self-collection testing options are available for syphilis. STDCheck’s page says it uses an RPR blood test at a testing center and uses a TPA test to confirm a positive result. Whichever route you use, a positive result needs follow-up with a clinician.