Finding the right tests…
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Finding the right tests…
Serology
TPHA checks your blood for antibodies that target the syphilis bacterium itself, Treponema pallidum, rather than the broader cell-damage markers a test like VDRL looks for. Because it's aimed specifically at the bacterium, TPHA is far less prone to the false positives that can affect VDRL, and it's typically used to confirm a reactive VDRL result rather than as the first test run. One real limitation is that TPHA generally stays reactive for life once you've been infected, even after complete treatment, so it can't tell your doctor whether an infection is active now or was successfully treated years ago — that judgement relies on your VDRL titre and clinical picture instead.
TPHA comes back as reactive or non-reactive, based on whether antibodies against Treponema pallidum are found in your blood. It's used to confirm syphilis in someone whose VDRL or RPR screening test has already come back reactive, including at low VDRL titres, where TPHA can still pick up a genuine infection. Because TPHA generally stays reactive for the rest of your life once you've had syphilis, a reactive result here doesn't distinguish a current infection from one treated long ago. A single blood sample is enough, with no special preparation needed.
TPHA detects antibodies your immune system makes specifically against Treponema pallidum, the bacterium that causes syphilis, using a method where the antibodies cause red blood cells coated with treponemal antigens to clump together. Because it targets the bacterium directly rather than general markers of cell damage, TPHA is more specific than a nontreponemal test like VDRL, which occasionally reacts to unrelated conditions.
Doctors typically run TPHA after a VDRL or RPR test comes back reactive, to confirm that the reaction is really syphilis rather than a false positive. Research on VDRL-reactive samples has found TPHA can still detect infection even at low VDRL titres that might otherwise be dismissed, which is part of why routine TPHA confirmation is recommended regardless of the VDRL titre.
Once TPHA turns reactive, it typically stays that way for life, even after syphilis has been fully treated. This means a reactive TPHA years after treatment doesn't mean the infection is still active — it simply shows you were infected at some point. To judge whether an infection is current or successfully treated, your doctor relies more on your VDRL titre trend and your treatment history than on TPHA alone.
VDRL can occasionally react to conditions unrelated to syphilis, so TPHA confirms that a reactive VDRL genuinely reflects a syphilis infection rather than a false positive.
Usually, yes. Most people who develop a reactive TPHA stay reactive for the rest of their lives, even after complete and successful treatment.
No. Because it stays reactive for life once you've been infected, TPHA can't distinguish an active infection from one treated years ago; your doctor uses your VDRL titre trend and history for that instead.
TPHA is more specific to syphilis, since it targets the bacterium directly rather than general markers of cell damage, which is why it's used to confirm a reactive VDRL result.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Yes. Research on VDRL-reactive samples has found TPHA can detect a genuine infection even at low VDRL titres, which is part of why routine confirmation is recommended regardless of titre.
No. No special preparation, including fasting, is needed before this blood draw.
This pattern can reflect a syphilis infection that was already treated in the past, since TPHA stays positive for life while VDRL tends to fall after treatment. Your doctor will look at your treatment history and symptoms to interpret it.