Can I order a treponema pallidum hemagglutination assay (TPHA) for a patient with a new penile ulcer?

TPHA for a new penile ulcer

Yes—order a treponemal test (TPHA/TP-PA) alongside a nontreponemal test (RPR or VDRL) immediately for a new penile ulcer, and add darkfield/DFA-TP if available. 1, 2

• Rationale (mortality/morbidity/QoL): Early diagnosis and treatment of syphilis prevents progression to neurosyphilis, cardiovascular disease, adverse pregnancy outcomes, and transmission. CDC guidelines endorse treponemal plus nontreponemal testing for ulcer evaluation; darkfield/DFA-TP from the lesion is definitive when available 1, 2.

Algorithm (actionable)

• If genital ulcer present now:

  • Order same-day:
    • Nontreponemal: RPR (quantitative titer) or VDRL 1, 2
    • Treponemal: TPHA/TP-PA (acceptable treponemal test) 1, 2
    • Lesion test if available: Darkfield or DFA-TP (definitive early) 1, 2
  • Also test for HSV (culture/antigen/PCR) and consider H. ducreyi where relevant; offer HIV testing per CDC 2.

• Interpretation/next steps:

  • RPR reactive + TPHA reactive → Presumptive syphilis; stage clinically; treat per stage; use RPR titer to follow response 1, 2.
  • RPR nonreactive + TPHA reactive → Possible very early infection, past treated infection, or false positive; repeat RPR in 1–2 weeks or obtain lesion darkfield/DFA-TP; manage based on exposure/stage risk 1, 2.
  • Isolated RPR reactive (TPHA nonreactive) → Likely biologic false positive; confirm with repeat treponemal assay (TP-PA/FTA-ABS) 1, 2.

Nuances and pitfalls

• TPHA is a treponemal test; once positive, it often remains positive for life and does not track treatment response—always pair with RPR/VDRL for staging and follow-up 1, 2.
• Early primary lesions can be seronegative on nontreponemal testing; lesion darkfield/DFA-TP improves timely diagnosis and prevents missed early disease 1, 2.
• Biologic false positives exist with nontreponemal tests; treponemal confirmation is required. Rare false-positive TPHA can occur; use a second treponemal assay if discordant 1.
• Ensure labs report full RPR endpoint titers (not “>1:32 only”) to enable management decisions 3.

Evidence notes

• CDC STI Guidelines (most authoritative and recent among provided guidelines) endorse two-test serologic approach and lesion-based definitive testing in early syphilis 1. Older CDC guidance aligns with this approach for genital ulcers 2.
• TPHA is an acceptable treponemal assay; historical accuracy data support its confirmatory role, but lifelong seropositivity limits its use for monitoring 1.