What is the syphilis screening test?
The screen used here is a Syphilis IgG/IgM antibody test by EIA (enzyme immunoassay), which is a treponemal antibody screen. It detects antibodies your immune system makes specifically against Treponema pallidum, the bacterium that causes syphilis.
IgM antibodies tend to appear early in an infection, and IgG antibodies follow and last longer. Screening for both means the test can pick up a recent infection as well as one from some time ago. Many UK laboratories use an EIA or a similar automated treponemal test as their first-line screen, because it's sensitive and suits large numbers of samples.
A non-reactive (negative) screen, taken at the right time after exposure, means no syphilis antibodies were found. A reactive (positive) screen is the starting point rather than a diagnosis: further tests then confirm the result and work out whether the infection is current or from the past.
What is the difference between treponemal and non-treponemal tests?
Treponemal tests detect antibodies against the syphilis bacterium itself. Non-treponemal tests detect antibodies linked to the tissue damage an active infection causes. The two do different jobs, which is why a full syphilis result often includes both.
Treponemal tests include the EIA screen, TPHA (Treponema pallidum haemagglutination assay) and TPPA (Treponema pallidum particle agglutination assay). Once you've made these antibodies, they typically persist for years, often for life, whether or not the infection was treated. So a positive treponemal test confirms you've been infected at some point, but on its own it can't say whether that infection is active now.
Non-treponemal tests include RPR (rapid plasma reagin) and VDRL. They measure antibodies to cardiolipin, a substance released when cells are damaged by infection. The result generally rises with a new or untreated infection and falls after successful treatment, so it's used to judge activity and monitor treatment.
Treponemal and non-treponemal tests compared
The table below sets out how the common syphilis tests differ.
What happens after a reactive screen?
In general UK laboratory practice, a reactive treponemal screen is followed by two more tests. A confirmatory treponemal test using a different method, such as TPPA or TPHA, checks that the screen is a true positive. An RPR then helps judge whether the infection is active.
The exact tests, and the order they're run in, vary between laboratories, so the names on a report can differ. Some reports also ask for a repeat sample to confirm the result. Whatever the names, a clinician reads them together, alongside your history, any symptoms and the date of any previous treatment.
What does the RPR titre mean, and why is it repeated?
RPR is usually reported as a titre, written as a ratio such as 1:4 or 1:16. The titre is the most diluted version of your sample that still tests positive, so 1:16 is a stronger result than 1:4. A higher titre generally points to more active infection.
A clinician repeats RPR after treatment because a falling titre is one of the main ways to confirm the treatment has worked. UK guidance looks for a sustained fall of at least two dilution steps (fourfold, for example from 1:16 to 1:4). A titre that rises, or that doesn't fall as expected, can prompt further assessment or retreatment, which our guide to syphilis treatment covers.
RPR is also how a clinician judges whether a new positive result, years after a treated infection, is a reinfection. Treponemal tests stay positive, so a rising RPR titre is what points to a new episode.
What if my treponemal test is positive but my RPR is negative?
This pattern is common in people who had syphilis and were treated successfully in the past. It can also appear in very early infection, before the RPR has risen, or in late infection.
It doesn't automatically mean an active infection, but it does need a clinician to interpret it against your history, any past treatment and any symptoms. If you've never been treated for syphilis, say so, because that changes how the result is read.
How testing works at our Harley Street clinic
A syphilis blood test is £85 plus a £50 blood draw (£135 total), with results in about 24 hours. If treatment is needed, it's an injection given at the clinic, usually at a follow-up visit once your results are back rather than on the day of testing. Treatment is charged separately at £275, with the consultation and medication included.
Syphilis is also part of every one of our screening packages, starting with Bronze at £250, which covers chlamydia, gonorrhoea, HIV and syphilis. Results for blood tests come back in about 24 hours, and urine and swab results within 3 working days. Many people test for HIV at the same visit; an HIV test is £75 plus a £50 blood draw (£125 total).
If you need every result the same day, the FAST Screen Simple (£350) covers HIV, syphilis, chlamydia and gonorrhoea, and the FAST Screen Complex (£450) adds hepatitis B and C, with all results in 6 hours. Our guide to same-day STI test results explains both.
You can walk in seven days a week at 117a Harley Street, and the visit is confidential, as with all of our private STI testing in London.
Book a syphilis test at 117a Harley Street: £85 plus a £50 blood draw (£135 total), results in about 24 hours.
References
- NHS: Syphilis
- BASHH: UK national guidelines on the management of syphilis
- NICE CKS: Syphilis
- UKHSA: Sexually transmitted infections surveillance data
