Short answer
Syphilis testing is usually blood-based, and CDC says a presumptive diagnosis requires both a nontreponemal test and a treponemal test. A single positive or negative result can be misleading without the full testing pattern, symptoms, exposure history, pregnancy status, HIV status, prior treatment, and follow-up plan.
RPR and VDRL are common nontreponemal tests. TP-PA, EIA, CIA, immunoblots, and rapid treponemal tests are examples of treponemal tests. The way these tests are combined matters as much as the individual result.
Common syphilis test types
| Test type | Examples | What it helps answer |
|---|---|---|
| Nontreponemal test | RPR, VDRL | Supports diagnosis, provides a titer, and helps monitor response after treatment. |
| Treponemal test | TP-PA, EIA, CIA, immunoblot, rapid treponemal tests | Helps detect antibodies specific to the syphilis bacterium, including current or prior infection. |
| Direct detection | Darkfield exam, some laboratory-developed PCR tests | May be used from lesion material in specialized settings, but blood tests are more common for screening. |
| CSF testing | CSF-VDRL and related cerebrospinal fluid tests | Used only in specific neurologic or eye/ear scenarios, not as routine screening. |
Traditional and reverse sequence testing
In a traditional algorithm, a nontreponemal test such as RPR or VDRL is used first, and a reactive result is confirmed with a treponemal test. In a reverse sequence algorithm, a lab starts with an automated treponemal immunoassay such as EIA or CIA, then reflexes to a quantitative nontreponemal test. If the pattern is discordant, CDC guidance describes using a different treponemal test, often TP-PA, to help adjudicate the result.
This is why portal snippets such as "RPR reactive," "RPR nonreactive," "TP-PA reactive," or "EIA reactive" can be hard to interpret alone. Prior treatment, a new exposure, low likelihood of infection, early infection, and false-positive results can create different follow-up paths.
How RPR and VDRL titers are used
RPR and VDRL titers are reported as dilution numbers, such as 1:2, 1:8, or 1:32. CDC says nontreponemal titers often correlate with disease activity and are used to monitor treatment response. A fourfold change, equal to two dilution steps, is usually needed to show a clinically significant difference.
RPR and VDRL numbers should not be compared directly as if they were the same test. CDC recommends sequential testing with the same method, preferably by the same laboratory, because methods can differ and RPR titers are often slightly higher than VDRL titers.
Who should consider screening
- Pregnant people should be screened early in pregnancy; some need repeat testing at 28 weeks and delivery.
- Sexually active gay, bisexual, and other men who have sex with men should test at least yearly for syphilis, with more frequent testing for some people.
- Sexually active people with HIV should be screened at initial HIV evaluation and at least annually thereafter.
- Some asymptomatic women and men should be screened based on local syphilis rates and risk factors.
- Anyone exposed to a partner with syphilis should seek clinical evaluation and testing guidance.
- People with sores, ulcers, rash, neurologic symptoms, eye symptoms, hearing symptoms, or unexplained compatible findings may need diagnostic evaluation rather than routine screening alone.
Pregnancy and congenital syphilis prevention
Pregnancy is a special situation because syphilis can pass to the fetus. CDC says pregnant people should be screened serologically at the first prenatal care visit, and repeat testing at 28 weeks and delivery is recommended for people in high-rate communities or at risk during pregnancy. Some states recommend screening three times during pregnancy for all pregnant people.
CDC also says no mother or newborn should leave the hospital without maternal serologic status documented at least once during pregnancy. A positive pregnancy screen needs careful follow-up because titers help monitor treatment response, and penicillin is the only known effective treatment for preventing congenital syphilis.
Positive, negative, or unclear results
A reactive result should not be ignored, but the next step depends on the full pattern. A reactive treponemal test may reflect current infection, prior treated infection, untreated past infection, or a false-positive pattern depending on the RPR/VDRL and second treponemal result. A nonreactive test can be falsely reassuring very early after exposure or when symptoms strongly suggest early syphilis.
Seek prompt clinical evaluation for neurologic symptoms, vision changes, eye pain, hearing loss, severe headache, stroke-like symptoms, pregnancy, known partner exposure, or sores, ulcers, rash, or mucous membrane lesions. CDC notes that CSF evaluation is used for specific neurologic findings, while ocular syphilis and otosyphilis symptoms require clinical evaluation with syphilis serology.
Questions to ask
- Was this a nontreponemal test, a treponemal test, or both?
- Was a quantitative RPR or VDRL titer reported?
- Was this a traditional algorithm or reverse sequence algorithm?
- If the results are discordant, was a second treponemal test such as TP-PA done?
- Could prior syphilis treatment, pregnancy, autoimmune disease, vaccination, injection drug use, HIV, or another infection affect interpretation?
- Do I need repeat testing because exposure may have been recent?
- Should I also test for HIV, chlamydia, gonorrhea, hepatitis, or other STIs?
- If pregnant or trying to become pregnant, when should repeat testing and treatment follow-up happen?
FAQ
Is one blood test enough to diagnose syphilis?
CDC says a presumptive diagnosis of syphilis requires two types of serologic tests: a nontreponemal test, such as RPR or VDRL, and a treponemal test, such as TP-PA, EIA, CIA, immunoblot, or a rapid treponemal test.
What is the difference between RPR and treponemal tests?
RPR and VDRL are nontreponemal tests that can be reported as titers and used to monitor treatment response. Treponemal tests detect antibodies more specific to the syphilis bacterium and often stay reactive after prior infection or treatment.
What does an RPR titer mean?
An RPR or VDRL titer is a dilution-based number that helps clinicians estimate activity and monitor response after treatment. CDC says a fourfold titer change, such as 1:16 to 1:4, is usually needed to show a clinically meaningful change.
Can syphilis tests stay positive after treatment?
Yes. CDC notes that most people with reactive treponemal tests remain reactive for life, while nontreponemal titers often decrease after treatment but may persist at low levels in some people.
Who should be screened for syphilis?
CDC recommends syphilis testing based on pregnancy, geography, HIV status, sexual practices, partner exposure, local epidemiology, and other risk factors. Pregnant people should be screened early, with repeat testing for some people later in pregnancy and at delivery.
When do syphilis symptoms need urgent evaluation?
Urgent clinical evaluation is important for neurologic symptoms, vision changes, eye pain, hearing loss, severe headache, stroke-like symptoms, pregnancy, a partner diagnosed with syphilis, or sores, ulcers, rash, or symptoms that could fit early syphilis.