When should a Rapid Plasma Reagin (RPR) test be drawn after syphilis exposure?

Timing of RPR Testing After Syphilis Exposure

RPR testing should be performed at baseline (time of exposure or diagnosis), 3 months, 6 months, 12 months, and 24 months after syphilis exposure to ensure adequate detection and treatment response monitoring.

Initial Testing Timeline

• Baseline testing: Perform RPR testing immediately upon known exposure or when symptoms appear
• Follow-up testing: The CDC recommends monitoring with nontreponemal serologic tests at:
  • 3 months post-exposure/treatment
  • 6 months post-exposure/treatment
  • 12 months post-exposure/treatment
  • 24 months post-exposure/treatment 1

Rationale for Testing Schedule

Early Detection Considerations

• RPR may be negative in very early primary syphilis, even when symptoms are present
• Approximately 20% of patients with primary syphilis may have negative RPR tests 2
• The 47-kDa T. pallidum antibody is detectable in all primary syphilis cases even when RPR is negative 2

Treatment Response Monitoring

• Treatment success is defined as a fourfold decrease in nontreponemal test titer 1
• This decrease should occur within:
  • 6 months for primary and secondary syphilis
  • 12-24 months for late-latent syphilis 1

Special Considerations

HIV Co-infection

• HIV-infected patients require more vigilant monitoring due to potentially altered serological responses
• More frequent monitoring (every 3 months) is recommended for HIV-infected individuals 1
• HIV-positive patients show higher rates of positive treponemal IgM tests in both initial infection (90.3%) and reinfection (71.4%) compared to HIV-negative individuals 3

Pregnancy

• All pregnant women should be screened for syphilis during early pregnancy
• High-risk pregnant women should be retested in the third trimester (ideally at 28-32 weeks) and at delivery 4
• Any woman delivering a stillborn infant after 20 weeks' gestation should be tested for syphilis 4

Post-Treatment Titer Variations

• Approximately 20% of patients may show a titer increase of at least one dilution in the 14 days after therapy 5
• This transient increase rarely affects assessment of therapeutic outcome (only about 3% of cases would be reclassified) 5
• The prozone phenomenon (falsely negative RPR in high-titer samples) is rare but important to consider when clinical suspicion is high but RPR is negative (0.5% of reactive samples) 6

Potential Pitfalls to Avoid

• Switching tests: Use the same nontreponemal test (RPR or VDRL) consistently during follow-up 1
• Relying on treponemal tests: These remain positive for life and cannot be used to monitor treatment response 1
• Misinterpreting serofast status: 15-20% of patients may remain "serofast" with persistent low, unchanging titers, which does not necessarily represent treatment failure 1
• Inadequate follow-up duration: Especially important in latent syphilis cases 1

Treatment Failure Indicators

• Failure to achieve fourfold decrease in titer within expected timeframe
• Sustained fourfold increase in titer after initial reduction
• Persistent or recurring clinical symptoms 1

Following this structured testing schedule will ensure appropriate monitoring for both initial detection of syphilis and evaluation of treatment response, ultimately reducing morbidity and mortality associated with untreated or inadequately treated syphilis.