What this test measures
TPHA (and its modern variant TPPA — T. pallidum particle agglutination) detects antibodies to T. pallidum by agglutination of sensitised red blood cells or particles. Highly specific for past or present syphilis. Like TPAb, remains positive for life — cannot be used to monitor treatment.
Why it matters
In the traditional Indian syphilis testing workflow, VDRL/RPR is the screen and TPHA is the confirmatory test. TPHA is cheap, manual, and widely available even in district-level labs. Reactive TPHA after reactive VDRL confirms syphilis infection (current or past). Modern centres are moving to automated ELISA / CMIA (TPAb) for first-line screening with VDRL confirmation (reverse algorithm), but TPHA remains a common confirmatory option.
How to prepare
No fasting. Random sample. Disclose any past syphilis treatment (TPHA stays positive for life), recent acute illness, pregnancy, and IV drug use history.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| TPHA (reactive / non-reactive; titre (1:80 to 1:10240+))[1] | Non-reactive | Non-reactive — no syphilis or very early primary infection (window 2–6 weeks). If clinically suspected, repeat 3 weeks later or use treponemal IgM. | Reactive — confirms exposure to T. pallidum. Active vs treated past infection is distinguished by quantitative VDRL/RPR titre, clinical staging, and treatment history. Reactive TPHA + non-reactive VDRL = past treated, very early, or late latent. |
TPHA in syphilis testing workflow
| VDRL/RPR | TPHA | Interpretation |
|---|---|---|
| Non-reactive | Non-reactive | No infection |
| Reactive | Reactive | Active or past treated — stage by titre / history |
| Reactive | Non-reactive | Biological false positive (BFP) — common in pregnancy, autoimmune |
| Non-reactive | Reactive | Past treated, late latent, or very early |
Frequently asked questions
What is the difference between TPHA and TPPA?
TPHA uses sensitised red blood cells; TPPA uses inert gelatin particles. Functionally equivalent; TPPA is slightly more sensitive and is replacing TPHA in newer labs.
Does TPHA test for active disease?
No — TPHA confirms exposure (past or present). Active infection is distinguished by clinical features and rising VDRL/RPR titres.
Why was VDRL ordered separately?
VDRL is the screen (cheap, sensitive in active disease, monitors treatment). TPHA is the confirmation (specific, but doesn't track treatment). They complement each other.
Will TPHA become negative after successful treatment?
No — TPHA usually stays positive for life. Use the VDRL/RPR titre to monitor treatment response (4-fold drop at 6–12 months = success).
Is TPHA reliable in pregnancy?
Yes — pregnancy does not cause false-positive TPHA. It is a reliable confirmatory test for antenatal screening.
Related HIV / STI tests
Tests commonly ordered alongside TREPONEMA PALLIDUM HAEMAGGLUTINATION, or that help interpret an unexpected result.
Sources & references
- CDC — Syphilis Laboratory Diagnosis · accessed 2026-05-30T00:00:00.000Z
- WHO — Syphilis Strategy · accessed 2026-05-30T00:00:00.000Z
- NACO India — Syphilis Diagnostic Workflow · accessed 2026-05-30T00:00:00.000Z
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