Syphilis Testing in Bengaluru: TPHA & Quantitative RPR
Comprehensive two-tier syphilis serology following CDC and Koneman diagnostic microbiology guidelines. Accurate distinction between active infection and past resolved illness.
Traditional vs Reverse Syphilis Screening Algorithms
Per the CDC STI Treatment Guidelines and Koneman Chapter 20, diagnostic laboratories employ two main serologic pathways to ensure clinical precision:
1. Traditional Algorithm
Begins with a quantitative non-treponemal screening test (RPR or VDRL). If reactive, the laboratory automatically reflexes to a specific treponemal confirmation test (TPHA or TPPA).
2. Reverse Sequence Algorithm
Begins with an automated treponemal immunoassay (EIA/CLIA). If reactive, the laboratory reflexes to a quantitative RPR to assess current disease activity and establish baseline titers.
Frequently Asked Questions
Why is one test not enough to diagnose syphilis?
No single serological test can reliably diagnose syphilis on its own. Non-treponemal tests (RPR/VDRL) can be falsely positive due to viral infections, lupus, pregnancy, or malaria. Treponemal tests (TPHA/TPPA) remain reactive for life even after a patient is completely cured. Therefore, CDC guidelines require BOTH tests together to differentiate active syphilis from a biological false positive or past successfully treated infection.
What is the difference between active syphilis and past treated syphilis?
In past treated syphilis, the treponemal test (TPHA) remains positive forever, but the non-treponemal test (RPR) becomes negative or drops to a stable low 'serofast' titer (e.g. 1:1 or 1:2). In active syphilis, both TPHA and RPR are reactive, and the RPR titer is typically significantly higher (e.g. 1:16, 1:32, 1:64) or rising.
How soon after a chancre appears can syphilis be detected by blood test?
Antibodies typically take 1 to 3 weeks after the appearance of the primary chancre (around 3 to 6 weeks after sexual exposure) to reach detectable levels in blood. If you have an active sore, darkfield microscopy or lesion PCR provides the earliest direct detection before blood antibodies form.