The TPHA (Treponema pallidum hemagglutination assay) is a blood test used as a specific confirmatory serology test for syphilis. It looks for antibodies your immune system makes against Treponema pallidum, the bacterium that causes syphilis. Because it detects treponemal antibodies (antibodies directed specifically at the syphilis germ), TPHA is commonly used to confirm syphilis when a screening test is positive.

In plain language: this test helps answer, “Has my body ever been exposed to the syphilis bacteria?” A positive TPHA usually means you have had a current or past infection with T. pallidum. Importantly, treponemal tests like TPHA can remain positive for many years, sometimes for life, even after successful treatment—so it may not tell whether the infection is active right now.

A negative TPHA suggests no evidence of treponemal antibodies. However, very early infection (before antibodies have developed) can sometimes yield a negative result, so your clinician may repeat testing if recent exposure is suspected.

TPHA results are typically interpreted together with other syphilis tests, especially a non-treponemal test such as RPR or VDRL, which helps estimate disease activity and is useful for monitoring response to treatment. In many labs, TPHA is ordered specifically for syphilis confirmation after an initial screening test (such as EIA/CLIA or RPR) is reactive.

A clinician may order TPHA when syphilis is suspected, when a screening test is positive, or when someone has risk factors for exposure. It is most often used as a confirmatory test to clarify whether a reactive screening result truly reflects syphilis infection.

Common reasons to do a TPHA (tpha) test include:

1) Confirming syphilis after a positive screening test
If an initial blood test suggests syphilis, TPHA helps confirm the presence of treponema antibody responses that are more specific to Treponema pallidum.

2) Symptoms that could suggest syphilis
Symptoms vary by stage and can be easy to miss. Testing may be recommended if you have:

• A painless genital, anal, or mouth sore (chancre)
• A widespread rash (often including palms or soles)
• Swollen lymph nodes, fever, sore throat, fatigue, muscle aches
• Unexplained neurologic symptoms (e.g., headache, vision/hearing changes), which may raise concern for neurosyphilis (usually evaluated with additional tests)

3) Sexual health screening and exposure concerns
TPHA may be used when a person has increased risk of sexually transmitted infections (STIs), such as:

• Unprotected sex or a new/multiple sexual partners
• A partner diagnosed with syphilis
• Living in an area or community with higher syphilis rates
• Diagnosis of another STI
• HIV infection (or situations where HIV risk is elevated)

4) Pregnancy and preconception testing
Syphilis screening is routinely recommended in pregnancy because untreated infection can be passed to the baby. TPHA may be used for confirmation if screening is reactive, helping guide timely treatment to reduce risks of miscarriage, stillbirth, premature birth, or congenital syphilis.

5) Evaluating past treatment or unclear history
If someone reports a past syphilis diagnosis or treatment but records are unclear, TPHA can help determine whether treponemal antibodies are present. Because it may stay positive long-term, your clinician will usually pair it with RPR/VDRL and clinical history to understand whether infection may be active or previously treated.

• Syphilis (primary, secondary, latent, or tertiary stages)
• Congenital syphilis (infection passed from mother to baby)
• Neurosyphilis (syphilis involving the brain or nervous system; requires additional evaluation)
• Ocular syphilis (eye involvement; requires urgent assessment)

• Confirming a suspected STI diagnosis (syphilis confirmation after a positive screen)
• Supporting safer sexual health decisions after possible exposure
• Protecting pregnancy and newborn health through timely detection and treatment
• Clarifying prior infection history when medical records are incomplete
• Reducing risk of long-term complications by enabling early diagnosis and linkage to care