TPHA (Syphilis Confirmation): What Positive Results Mean

When I tell a patient that their routine syphilis screening has come back positive, the next question is almost always: “Is it really syphilis?” That’s where the Treponema pallidum Hemagglutination Assay (TPHA) comes in. This is not a screening test — it’s the confirmation step, the one that separates a true infection from a false alarm. In this article, I’ll walk you through what TPHA measures, how to interpret the results, and what happens next after a reactive TPHA.

What Is the TPHA Test?

The TPHA test detects antibodies that are specifically produced against Treponema pallidum, the bacterium that causes syphilis. Unlike non-treponemal tests (like VDRL or RPR) that can give false positives due to pregnancy, autoimmune conditions, or infections, TPHA is a treponemal test — it looks for antibodies directed at the actual syphilis bacteria.

Once you have had syphilis (even if treated successfully), TPHA usually remains positive for life. That means it is not used to monitor cure — it is a diagnostic stamp of past or present infection.

When Is TPHA Ordered?

In my practice, I order TPHA as a confirmatory test when a patient’s non-treponemal screening (e.g., RPR) is reactive. It is also part of the workup for:

• Unexplained rash, particularly on the palms and soles
• Genital ulcers or lesions
• Neurological symptoms suspicious for neurosyphilis
• Routine screening during pregnancy (in some countries)
• Evaluation of stillbirth or congenital syphilis

TPHA Reference Ranges (Interpretation)

The TPHA result is reported as either non-reactive (negative) or reactive (positive). In some labs, a titre is given (e.g., 1:80, 1:160, 1:320) — the titre indicates the concentration of antibodies. A higher titre often suggests active infection, while low titres (1:80 or 1:160) can be seen in old treated infections.

What Does a Positive TPHA Mean?

A positive TPHA means you have been infected with syphilis at some point in your life. It does not tell us whether the infection is currently active. To determine activity, we also check a non-treponemal test like RPR or VDRL. If that is also positive, the infection is likely active and requires treatment. If the RPR is negative but TPHA is positive, you likely had syphilis in the past that was treated or resolved spontaneously (though spontaneous cure is rare).

TPHA During Pregnancy

Every pregnant woman should be screened for syphilis in the first trimester — and again in the third trimester if she is at high risk. A reactive TPHA in pregnancy demands immediate evaluation because untreated syphilis can cross the placenta and cause congenital syphilis, which can lead to stillbirth, bone deformities, blindness, or developmental delay. In my clinic, we immediately treat with penicillin (the only recommended therapy in pregnancy) and follow the baby after birth.

Can TPHA Be False Positive?

Yes, but it is much rarer than with non-treponemal tests. False-positive TPHA results can occur in:

• Lyme disease (cross-reacting antibodies)
• Yaws or pinta (other treponemal infections)
• Systemic lupus erythematosus (rare)
• Human immunodeficiency virus (HIV) co-infection (though usually true positive)

If a false positive is suspected, a second treponemal test (e.g., FTA-ABS) is performed to confirm.

What Happens After a Reactive TPHA?

If your TPHA is reactive and your RPR is also positive, the next steps are:

1. Clinical staging: Physical exam (rash, lesions, neurological signs) to determine the stage of syphilis.
2. Treatment: Benzathine penicillin G injection (a single dose for early syphilis, three doses for late latent).
3. Follow-up: Repeat RPR at 3, 6, 12 months to ensure the titre drops (indicating successful treatment).
4. Partner notification: Sexual partners from the past 3–12 months (depending on stage) should be tested and treated.
5. HIV testing: Syphilis infection increases the risk of HIV transmission; testing is recommended.

Is TPHA Tested on Blood or Serum?

TPHA is performed on a blood sample — usually a standard venous blood draw (serum). No special preparation is needed, but it is typically done alongside other syphilis serologies.

How Long After Exposure Does TPHA Turn Positive?

Most people develop detectable antibodies 4–6 weeks after infection. In the very earliest stage (primary syphilis), the TPHA may still be negative even if the chancre is present. That’s why I always advise repeating the test in 2–4 weeks if the suspicion is high and the initial result is negative.

Bottom Line

TPHA is the gold standard confirmatory test for syphilis. A positive result is not a life sentence — syphilis is completely curable with penicillin. The key is early detection and treatment. In my years of practice, I have treated hundreds of patients with syphilis, and almost all of them go on to live normal, healthy lives after a simple course of antibiotics. If you have a reactive TPHA, please see an infectious disease or sexual health specialist promptly.