Syphilis Antibody, Treponemal
Looks for antibodies to the bacterium that causes syphilis. It usually stays positive for life after an infection, even a treated one.
AI-verified against cited sources. Awaiting expert reviewAlso called TP-PA, TPPA, TPHALOINC 22587-0
What it is
Syphilis is an infection caused by the bacterium Treponema pallidum. This blood test looks for antibodies your immune system makes against that bacterium, which is why it is called a treponemal test. Labs use several methods, including immunoassays (EIA or CIA), particle agglutination (TP-PA or TPHA) and fluorescent tests (FTA-ABS), and they report the result as reactive or non-reactive. It is usually read together with a non-treponemal test such as the RPR.
Why it matters
Treponemal antibodies appear within weeks of infection and usually stay detectable for the rest of a person's life, even after treatment. So a reactive result can mean a current infection or an old, treated one, and the test alone can't tell which. Clinicians read it with an RPR or VDRL result, your history and any symptoms. It is part of routine prenatal and sexually transmitted infection testing. It is not used to check whether treatment worked.
If it’s low
A non-reactive result means no syphilis antibodies were found. Very early infection can be missed, because antibodies take a few weeks to appear.
Common causes
- No past or current syphilis infection
- An infection too recent for antibodies to be detectable yet
What can help
- If you may have been exposed recently, ask your clinician about testing again after a few weeks
If it’s high
A reactive result means antibodies to the syphilis bacterium were found. This can be a sign of a current infection, of a past infection that was treated, or occasionally of a false-positive result, especially in people with a low chance of infection. Your clinician will use more testing and your history to sort out which.
Common causes
- A current syphilis infection
- A past syphilis infection that was treated, since treponemal tests usually stay reactive for life
- A false-positive screening result, which is more likely in people at low risk
- Related infections such as yaws, pinta or bejel, which are uncommon in many countries
What can help
- Ask your clinician which follow-up tests are needed, such as an RPR or VDRL, or a second treponemal test
- Share any history of past syphilis testing or treatment
- Ask whether testing for other sexually transmitted infections makes sense
What can affect your result
- Time since infection: antibodies take a few weeks to appear
- A past treated infection, which usually stays reactive for life
- The method used: immunoassay (EIA or CIA), TP-PA, TPHA or FTA-ABS
- How common syphilis is in the group tested, which changes how often a positive is a false positive
- A single reactive screening result in someone at low risk of infection can be a false positive, so labs and clinicians often confirm it with a second, different test (CDC).
- Related infections in the same bacterial family (yaws, pinta and bejel) can also make treponemal tests reactive, and the FTA-ABS cannot tell them apart from syphilis (Quest).
- Grossly hemolyzed or very fatty (lipemic) samples may be rejected (Quest).
Treponemal antibodies appear a few weeks after infection (Quest says the FTA-ABS turns reactive 4 to 6 weeks after infection) and usually stay reactive for life, even after successful treatment (CDC).
When to talk to a clinician
A reactive result is not an emergency, but it needs follow-up with a clinician soon. Contact a clinician promptly if you have a painless sore, a new rash (especially on the palms or soles), changes in vision or hearing, or a severe headache or confusion. If you are pregnant, tell your prenatal clinician about a reactive result right away.
Questions you could ask
- How will this result be read together with my other syphilis test results?
- Which follow-up tests do I need, and how soon?
- Could this be an old infection that was already treated, or a false positive?
- Should I be tested for other infections as well?
- If I may have been exposed recently, should I be tested again?
Questions people ask
If I was treated for syphilis, will this test stay positive?
Usually yes. The CDC notes that most people with a reactive treponemal test stay reactive for the rest of their lives, whether or not they were treated. That is why this test isn't used to follow treatment. Clinicians use a different test, such as the RPR, for that.
My screening test is reactive but my RPR is negative. What does that mean?
This pattern is known in the reverse testing approach. It can come from an old treated infection, a very early or very old infection, or a false-positive screen. Labs usually run a second, different treponemal test to help sort it out, and your clinician will read it with your history.
How is this different from an RPR?
This test looks for antibodies aimed at the syphilis bacterium and usually stays positive for life. The RPR (and VDRL) looks for a different kind of antibody that tends to follow disease activity, so clinicians use it to follow treatment. The two are usually read together.
Show the science and sources
For clinicians and researchers
Treponemal tests detect antibodies to T. pallidum antigens. CDC notes that most people with a reactive treponemal test stay reactive for the rest of their lives regardless of treatment or disease activity, and that treponemal titers do not predict treatment response. The traditional algorithm screens with a non-treponemal test (RPR or VDRL) and confirms with a treponemal test. The reverse sequence algorithm screens with an automated treponemal immunoassay (EIA or CIA) and reflexes to a non-treponemal test; it can find previously treated infection, untreated infection and false positives in low-prevalence settings. Quest and ARUP describe TP-PA as a confirmatory treponemal test, and ARUP calls FTA-ABS not an optimal confirmation test. ARUP's IgG ELISA reports an index value: 0.9 IV or less negative, 1.0 IV equivocal, 1.1 IV or more positive. TP-PA and TPHA may print a titer, which is not used to monitor treatment. Quest's FTA-ABS note says it becomes reactive 4 to 6 weeks after infection and does not distinguish syphilis from yaws, pinta or bejel. Results are qualitative (Mayo and Quest reference: non-reactive or negative).
LOINC 22587-0 (primary), 24110-9, 47238-1, 51838-1, 24312-1, 17726-1, 22590-4. Specimen: serum.
Sources
- Sexually Transmitted Infections Treatment Guidelines, 2021: Syphilis, Centers for Disease Control and Prevention (2021)
- About Syphilis, Centers for Disease Control and Prevention (2025)
- Treponema pallidum Antibody, Immunoassay (test code 13646), Quest Diagnostics
- Treponema pallidum Antibody, Particle Agglutination (test code 653), Quest Diagnostics
- FTA-ABS (test code 4112), Quest Diagnostics
- Treponema pallidum Antibody by TP-PA (test 0050777), ARUP Laboratories
- Treponema pallidum Antibody, IgG by ELISA (test 0050920), ARUP Laboratories
- Treponema pallidum Antibody, IgG by IFA (FTA-ABS), Serum (test 0050477), ARUP Laboratories
- Syphilis IgG Enzyme Immunoassay, Serum (NSYPH), Mayo Clinic Laboratories (via testcatalog.org)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.