What this test measures
VDRL (Venereal Disease Research Laboratory) and RPR (Rapid Plasma Reagin) are non-treponemal tests that detect antibodies against cardiolipin–lecithin–cholesterol antigens. Both are functionally equivalent, screen the same antibody class, and are reported as reactive / non-reactive with titre (1:1, 1:2, 1:4, ...). They are CHEAP and good for SCREENING and TREATMENT MONITORING but not specific — biological false positives occur in many conditions.
Why it matters
India has ongoing syphilis transmission, with NACO reporting persistent positivity in ANC screening (~0.3-2%) and higher rates among MSM and FSW groups. WHO recommends universal antenatal screening — congenital syphilis is a major preventable cause of stillbirth, prematurity, and neonatal mortality. Routine RVS panel (Reactive Syphilis Screen) is part of antenatal, blood-donation, premarital, pre-organ-transplant, and high-risk population screening. Modern WHO-recommended workflow is "reverse algorithm" — start with treponemal test (TPHA, ELISA, CMIA) and confirm reactive results with VDRL/RPR; the older "traditional algorithm" (VDRL → confirm with TPHA) is still used in many Indian labs.
How to prepare
No fasting required. Random sample. Disclose pregnancy, recent vaccination, recent acute illness, current malaria / TB / autoimmune disease, IV drug use. Note that biological false positives (transient) commonly occur with pregnancy, recent viral infection, TB, malaria, leprosy, SLE, antiphospholipid syndrome, advanced age, and recent immunisation.
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 |
|---|---|---|---|
| VDRL / RPR (titre (1:1 to 1:512+))[1][2] | Non-reactive | Non-reactive — no syphilis or very early infection (window period 1–6 weeks). If high suspicion, repeat in 3 weeks or add treponemal test. | Reactive — confirm with treponemal test (TPHA, FTA-ABS, or CMIA). Untreated syphilis: titre usually rises from primary to secondary (1:32-1:128), then falls in latent stages. Treated syphilis: 4-fold (2-dilution) drop in titre at 6-12 months indicates successful treatment. Stable low titre (1:1-1:4) without 4-fold change = "serofast state" — not necessarily active disease. Biological false positives (BFP): usually low titre (<1:8), confirmed by negative treponemal test. |
VDRL/RPR interpretation in syphilis workup
| VDRL/RPR | Treponemal test | Interpretation |
|---|---|---|
| Non-reactive | Non-reactive | No infection (or window period — repeat in 3 wks if high risk) |
| Reactive | Reactive | Active or past treated syphilis — staging by titre + history |
| Reactive (low titre) | Non-reactive | Biological false positive (BFP) |
| Non-reactive | Reactive | Past treated, very early, or late latent syphilis |
| Reactive (rising titre) | Reactive | Active untreated or reinfection |
| Reactive (4-fold drop after treatment) | Reactive (persists) | Successful treatment |
Frequently asked questions
Do I need to fast?
No.
Will a positive test mean I have syphilis?
Not necessarily. Reactive VDRL / RPR must be confirmed with a treponemal test (TPHA, FTA-ABS) to rule out biological false positives, which occur in pregnancy, autoimmune disease (lupus, antiphospholipid), TB, malaria, viral infections, and old age.
What is the prozone phenomenon?
In high-titre syphilis (often secondary or HIV co-infected), excess antibody can paradoxically give a false-negative qualitative test — the lab must dilute the sample to reveal true positivity. If you suspect syphilis despite negative VDRL, ask for prozone-checked or treponemal testing.
How long after treatment does the titre fall?
A 4-fold drop (e.g. 1:64 → 1:16) at 6–12 months indicates successful treatment. Some patients enter "serofast state" with persistent low titre that doesn't need re-treatment.
Why did my doctor order both VDRL and TPHA?
VDRL screens; TPHA confirms. Combined testing avoids both false-positive treatment and missed disease.
Is syphilis treatable?
Yes. Penicillin G (benzathine penicillin IM) is the standard treatment. Early syphilis: single dose. Late latent: weekly for 3 weeks. Neurosyphilis: IV penicillin for 10–14 days. Treatment is highly effective.
Related HIV / STI tests
Tests commonly ordered alongside VDRL (RPR) FOR SYPHILIS, 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 Surveillance · accessed 2026-05-30T00:00:00.000Z
- IUSTI — Syphilis Guideline · accessed 2026-05-30T00:00:00.000Z
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