A 26-year-old man has a painless penile ulcer with indurated edges for 3 weeks. VDRL is reactive at 1:32 dilution. TPHA is also reactive. He denies prior history of syphilis or treatment. What is the interpretation of these results?
- A Biological false positive — VDRL 1:32 with positive TPHA cannot occur in BFP
- B Active syphilis (VDRL reactive with high titre + TPHA positive — confirms active treponemal infection in a previously untreated patient) ✓
- C Past treated syphilis — VDRL and TPHA both remain positive for life
- D Neurosyphilis — CSF FTA-ABS is needed before this result can be interpreted
Correct answer: B. Active syphilis (VDRL reactive with high titre + TPHA positive — confirms active treponemal infection in a previously untreated patient)
Explanation
A reactive VDRL at high titre (≥1:8) combined with a reactive TPHA/TPPA in a previously untreated patient with a primary chancre is diagnostic of active syphilis. VDRL (non-treponemal) rises in active disease and falls with treatment, serving as a treatment response marker. TPHA (treponemal test) confirms true Treponema pallidum antibody and rules out biological false positive (BFP), which only occurs with non-treponemal tests. BFP (e.g., from SLE, pregnancy) gives reactive VDRL but negative treponemal tests.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.