Why Does Syphilis Require Two Different Blood Tests?
Medically reviewed by our MD Laboratory Director (a role required by CLIA; the director's name is on file in the CMS CLIA database, #45D2048957, and can be verified independently) · Editorial policy
One reactive test is not a diagnosis. Syphilis serology is a two-step algorithm.CLIA #45D2048957 · CAP #8722734 · Same-day results · Walk-ins welcome
Because either test alone misleads. Nontreponemal tests (RPR, VDRL) give a titer — a number that rises with active infection and falls with successful treatment — but they produce false positives in pregnancy, autoimmune disease and other conditions. Treponemal tests (TP-PA, EIA) are specific to the organism but generally stay reactive for life, so they cannot tell current infection from a treated one. You need both.
Not sure what you need? Text us and we will set it up.
📱 Text (713) 832-8892 📞 Call (713) 266-0808
📱 Text (713) 832-8892 📞 Call (713) 266-0808
3707 Westcenter Dr Suite 100, Houston, TX 77042 · Walk-ins welcome
What each test does
| Nontreponemal (RPR / VDRL) | Treponemal (TP-PA / EIA) | |
|---|---|---|
| Measures | Antibody titer that tracks disease activity | Antibodies specific to T. pallidum |
| After treatment | Titer falls — this is how cure is monitored | Usually stays reactive for life |
| False positives | Yes — pregnancy, autoimmune disease, some infections | Rare |
| Role | Screening and follow-up | Confirmation |
A treponemal test that stays positive for life is why "I tested positive for syphilis again" often means "I was treated years ago," not "I have it now." The titer is what distinguishes them.
Follow-up is part of treatment
After treatment with benzathine penicillin G, CDC expects the nontreponemal titer to decline over months. That follow-up is the evidence the treatment worked — which is why syphilis is not a one-visit-and-forget diagnosis.
We name drugs, never doses. Treatment statements follow CDC guidance; the physician decides what you actually take.
Same day, start to finish. Sample by 1:00 PM → results at 4:30 PM → if treatment is clinically appropriate, a licensed physician in our partner network sees you between 4:30 and 6:00 PM, a few minutes away. That window is reserved for patients tested here, and your slot is held the moment we take your sample — the slot is held, not hunted. On your own, a same-day appointment is nearly impossible; at an urgent care, you wait in the queue. STAT: ~2 hours, sample in by 3:00 PM.
FAQ
- I have a reactive screen. Do I have syphilis?
- Not established yet. Confirmatory testing decides it. Do not start treatment on a single reactive screen.
- Why did my titer not go to zero?
- A serofast state can persist. Interpretation belongs to the physician, in the context of your history.
- Is syphilis curable?
- Yes, with penicillin per CDC. Damage from late-stage disease is not reversible — which is the argument for testing.
- Do you offer the confirmatory test?
- Yes. Come in and we will run the correct algorithm rather than a single number.
Not sure what you need? Text us and we will set it up.
📱 Text (713) 832-8892 📞 Call (713) 266-0808
📱 Text (713) 832-8892 📞 Call (713) 266-0808
3707 Westcenter Dr Suite 100, Houston, TX 77042 · Walk-ins welcome
References
- CDC — STI Treatment Guidelines, 2021
- CDC — Syphilis (Detailed Fact Sheet)
- Our CLIA #45D2048957 and CAP #8722734 credentials — verify them yourself
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