QUICK ANSWER
RPR, Rfx Qn RPR/Confirm TP is a syphilis screening panel that combines an initial RPR screen with automatic reflex to a quantitative titer and confirmatory treponemal antibody test if the screen is reactive.
What each part of the test name means:
| Abbreviation | Full meaning |
|---|---|
| RPR | Rapid Plasma Reagin — the initial syphilis antibody screen |
| Rfx | Reflex — the lab automatically runs the next test if the prior result is reactive |
| Qn | Quantitative — a titer (dilution measurement) of antibody level |
| Confirm TP | Confirmatory Treponema pallidum test — a specific treponemal antibody test (TP-PA or FTA-ABS) to confirm true syphilis vs. false positive |
Most common result — Non-Reactive:
| Result | Meaning |
|---|---|
| Non-Reactive | No syphilis antibodies detected — normal result, syphilis unlikely |
| Reactive | Syphilis antibodies detected — reflex tests are performed to confirm |
Key takeaway: A non-reactive result on RPR, Rfx Qn RPR/Confirm TP means syphilis is very unlikely. Most people seeing this result on their LabCorp report have nothing to be concerned about.
Quick result lookup:
| Your result | What it usually means |
|---|---|
| Non-Reactive | No syphilis antibodies detected — normal result |
| Reactive + Confirm TP Reactive | Consistent with current or previous syphilis infection (clinical evaluation needed) |
| Reactive + Confirm TP Non-Reactive | Biological false positive more likely — syphilis unlikely |
| Reactive + Confirm TP not yet resulted | Reflex testing in progress |
WHAT DOES NON-REACTIVE MEAN ON THIS TEST?
Non-reactive is the normal, expected result. It means the RPR screen did not detect reagin antibodies — the antibodies that appear in response to syphilis infection. A non-reactive result indicates:
- No current syphilis infection is detected
- No significant reagin antibody response is present
- No reflex testing (quantitative titer or Confirm TP) was performed — because it was not triggered
A non-reactive result effectively ends the testing cascade. No further interpretation is needed.
Important nuance: RPR can occasionally be negative (non-reactive) very early in syphilis infection — within the first few weeks before antibodies have developed. If there is genuine concern about very recent exposure, retesting in 2–4 weeks may be recommended by your clinician.
WHAT DOES REACTIVE MEAN — AND WHAT HAPPENS NEXT?
A reactive RPR screen means the test detected reagin antibodies. This triggers the reflex cascade — the lab automatically performs additional tests to determine whether the reactive result represents:
- True syphilis infection (current or past)
- Biological false positive — a reactive RPR not caused by syphilis
The reflex cascade:
| Step | Test | Triggered by |
|---|---|---|
| 1 | RPR screen (qualitative) | Always performed |
| 2 | RPR Qn (quantitative titer, e.g., 1:2, 1:4, 1:8) | RPR screen reactive |
| 3 | Confirm TP (TP-PA or FTA-ABS) | RPR screen reactive |
Interpreting the reflex results:
| RPR screen | RPR Qn | Confirm TP | Interpretation |
|---|---|---|---|
| Non-reactive | Not performed | Not performed | No syphilis antibodies — normal |
| Reactive | ≥ 1:1 | Non-reactive | RPR positive but TP negative — biological false positive; syphilis unlikely |
| Reactive | ≥ 1:1 | Reactive | Both positive — consistent with current or past syphilis infection |
WHAT IS "CONFIRM TP"?
Confirm TP refers to a confirmatory treponemal antibody test — the second line of testing triggered when the RPR screen is reactive.
While the RPR measures non-treponemal antibodies (reagin), the Confirm TP measures antibodies that are specific to Treponema pallidum — the bacterium that causes syphilis. This distinction matters because:
- RPR can be falsely reactive in many conditions unrelated to syphilis (biological false positives)
- Confirm TP tests are far more specific — a positive Confirm TP with a positive RPR strongly confirms syphilis exposure
Common Confirm TP tests:
- TP-PA (Treponema pallidum Particle Agglutination) — the most commonly used confirmatory test on the LabCorp RPR, Rfx Qn RPR/Confirm TP panel
- FTA-ABS (Fluorescent Treponemal Antibody Absorption) — older gold standard, now less commonly used
- EIA/CIA (Enzyme or Chemiluminescent Immunoassay for T. pallidum IgG/IgM) — used in reverse screening algorithms
Importantly: Treponemal antibody tests (Confirm TP) typically remain positive for life after syphilis infection, even after successful treatment. A reactive Confirm TP in someone who has been treated for syphilis in the past is expected and does not indicate reinfection.
WHAT IS "RFX" ON A LAB REPORT?
Rfx stands for "reflex" — a laboratory instruction meaning the test will automatically cascade to the next step if the prior result meets a predefined threshold.
On this panel:
- If RPR screen = Non-Reactive → no reflex occurs → report shows only the non-reactive result
- If RPR screen = Reactive → reflex occurs → lab automatically adds RPR Qn (titer) and Confirm TP
You did not separately order the quantitative titer or the confirmatory test — the lab performed them automatically based on the reactive screen result. This is standard syphilis testing protocol.
WHAT ARE BIOLOGICAL FALSE POSITIVES?
A biological false positive RPR is a reactive RPR screen result that is not caused by syphilis. The RPR is a non-specific test and can be triggered by various conditions:
- Pregnancy — one of the most common causes of low-titer biological false positives
- Autoimmune diseases — particularly systemic lupus erythematosus (SLE) and antiphospholipid syndrome
- Viral infections — EBV (mononucleosis), hepatitis, HIV
- IV drug use
- Advanced age
- Other spirochetal infections (Lyme disease, leptospirosis, yaws)
The confirmatory TP test (Confirm TP) distinguishes biological false positives from true syphilis. If RPR is reactive but Confirm TP is non-reactive → biological false positive is the likely explanation, and true syphilis is unlikely.
WHAT IS THE RPR TITER AND WHY DOES IT MATTER?
When the RPR screen is reactive, the quantitative titer (Qn) measures the level of antibody as a dilution ratio — expressed as 1:1, 1:2, 1:4, 1:8, 1:16, 1:32, etc.
What titer levels indicate:
| RPR titer | General interpretation |
|---|---|
| 1:1 | Borderline reactive — may indicate biological false positive or very early/late infection |
| 1:2–1:4 | Low titer — early, late latent, or treated syphilis; also seen in biological false positives |
| 1:8–1:16 | Moderate titer — active infection more likely |
| 1:32 or higher | High titer — consistent with active or recent syphilis infection |
Titer is used to monitor treatment response: After successful treatment, RPR titers should decline 4-fold (e.g., from 1:16 to 1:4) within 6–12 months. A rising titer suggests reinfection or treatment failure. A persistently low titer after treatment ("serofast") is common and does not necessarily indicate treatment failure.
WHEN TO FOLLOW UP
Discuss your result with a clinician if:
- RPR screen is reactive — regardless of Confirm TP result, clinical follow-up is needed
- Both RPR and Confirm TP are reactive — evaluation for treatment and partner notification is needed
- RPR is reactive but Confirm TP is non-reactive — biological false positive workup may be recommended, particularly if autoimmune disease or pregnancy is present
- You are pregnant and have a reactive RPR — urgent evaluation is required regardless of titer level
BOTTOM LINE
Bottom line: RPR, Rfx Qn RPR/Confirm TP (LabCorp 012005) is a syphilis screening panel. Non-reactive means no syphilis detected — the normal result. Reactive triggers automatic reflex testing: a quantitative titer and a confirmatory treponemal antibody test (Confirm TP). If both the RPR and Confirm TP are reactive, current or past syphilis is likely. If only the RPR is reactive with a non-reactive Confirm TP, a biological false positive is the probable explanation.
RPR, Rfx Qn RPR/Confirm TP
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Frequently Asked Questions
Can RPR be non-reactive if I have syphilis?
Is syphilis curable?
What does non-reactive mean on RPR, Rfx Qn RPR/Confirm TP?
What does "Rfx" mean on a lab report?
What does "Confirm TP" mean?
What does "Qn" mean in this test?
What is a biological false positive RPR?
I was treated for syphilis — why is my Confirm TP still reactive?
What is LabCorp test 012005?
What does RPR stand for?
All our content is backed by peer-reviewed studies, academic research, and trusted medical sources. We’re committed to accuracy and transparency — see our editorial policy for details.
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Sexually Transmitted Infections Treatment Guidelines, 2021
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Novel Treponema pallidum serologic tests: a paradigm shift in syphilis screening for the 21st century
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Sexually transmitted diseases treatment guidelines, 2015