Treatment for Reactive TP-A (FTA-ABS) with Non-Reactive RPR
Patients with a reactive treponemal test (TP-A/FTA-ABS) and non-reactive nontreponemal test (RPR) should receive treatment for late latent syphilis with benzathine penicillin G 2.4 million units IM weekly for 3 weeks.
Understanding the Serologic Pattern
This serologic pattern (TP-A+/RPR-) can represent several clinical scenarios:
- Previously treated syphilis with serologic scar (most common) 1
- Late latent syphilis or tertiary syphilis with waning nontreponemal antibodies 2
- Early syphilis before nontreponemal antibody development (rare) 1
- False-positive treponemal test (less likely with FTA-ABS) 2, 3
Diagnostic Interpretation
The sensitivity of nontreponemal tests varies by stage of infection:
- Primary syphilis: 70-80% sensitivity 2
- Secondary syphilis: 97-100% sensitivity 2
- Late latent syphilis: 61-76% sensitivity 2
- Tertiary syphilis: 47-64% sensitivity 2
Therefore, a non-reactive RPR with reactive TP-A is commonly seen in late syphilis, where nontreponemal antibodies have declined over time 2.
Treatment Recommendations
For patients with no documented adequate treatment history:
- Administer benzathine penicillin G 2.4 million units IM once weekly for 3 weeks (total 7.2 million units) 2, 4
- For penicillin-allergic patients: doxycycline 100 mg orally twice daily for 28 days 5
For patients with documented adequate prior treatment:
- No additional treatment is needed as this likely represents a serologic scar 1
- Treponemal tests typically remain reactive for life in most patients regardless of treatment 1
Special Considerations
HIV Co-infection
- Some HIV-infected patients may have atypical serologic patterns 2
- Standard serologic tests remain accurate for most HIV patients 2
- Consider additional testing in cases with clinical suspicion despite discordant serology 6
Neurosyphilis Evaluation
- Consider CSF examination if neurological symptoms are present 7
- VDRL-CSF is highly specific but insensitive for neurosyphilis 2, 7
- CSF leukocyte count >5 WBCs/mm³ is a sensitive indicator for neurosyphilis 7
Common Pitfalls
- Failing to obtain a thorough history of prior syphilis treatment 1
- Misinterpreting the discordant pattern as a false positive without considering late syphilis 2
- Using only one type of test for diagnosis (both treponemal and nontreponemal tests are needed) 1
- Comparing titers between different test types (VDRL vs RPR) 1
- Relying on treponemal tests to assess treatment response (nontreponemal tests should be used) 1
Follow-up Recommendations
- No follow-up serologic testing is needed if treating presumed late latent syphilis with documented prior adequate treatment 2
- For newly diagnosed and treated late latent syphilis, clinical follow-up is recommended, but serologic response may be minimal 2
- Treponemal tests typically remain reactive for life and should not be used to monitor treatment response 1