What is the syphilis screening test?
The syphilis 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 recent infection as well as infection from some time ago. Many UK laboratories use an EIA or a similar automated treponemal test as their first-line screen, because it is 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 not a diagnosis on its own. It is the point at which further tests are done to confirm the result and to 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 groups 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 have made these antibodies, they typically persist for years, often for life, whether or not the infection was treated. A positive treponemal test confirms that you have been infected with syphilis at some point. It does not, by itself, 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 is used to judge activity and to 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 a confirmatory treponemal test using a different method, such as TPPA or TPHA, and by an RPR. The confirmatory test checks that the screen result is a true positive; the RPR helps judge whether the infection is active.
The exact tests and the order they are run in vary between laboratories, so the names on a report can differ. Some reports also include 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 that 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 rising titre, or one that does not fall as expected, can prompt further assessment or retreatment, which is covered in our guide to syphilis treatment.
RPR is also the test used to judge whether a new positive result years after a treated infection is a reinfection. Because treponemal tests stay positive, a rising RPR titre is what points towards 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 be seen in very early infection, before the RPR has risen, or in late infection. It does not automatically mean an active infection is present, but it needs a clinician to interpret it against your history, any past treatment and any symptoms. If you have never been treated for syphilis, tell the clinician, because that changes how the result is read.
How testing works at our Harley Street clinic
A syphilis blood test at Sexual Health Clinic London is £85 plus a £50 blood draw (£135 total), with results in as little as 24 hours. The test is a Syphilis IgG/IgM antibody screen by EIA. If treatment is needed, it is given by injection 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 testing is also included in every one of our screening packages, starting with Bronze at £250, which covers chlamydia, gonorrhoea, HIV and syphilis. Many people test for HIV at the same visit; an HIV test is £75 plus a £50 blood draw (£125 total). 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 as little as 24 hours.
References
- NHS: Syphilis
- BASHH: UK national guidelines on the management of syphilis
- NICE CKS: Syphilis
- UKHSA: Sexually transmitted infections surveillance data
