The routine test for Syphilis looks for the presence of antibodies in the blood.
For those experiencing ‘chancres’ which are suspected to be Syphilis may require a Syphilis swab which looks for the the DNA of Treponema pallidum (the bacteria that causes Syphilis).
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How is Syphilis diagnosed?
There are 2 different types of tests to diagnose or rule out Syphilis.
(1) Syphilis Blood Test
The Syphilis blood test looks for different antibodies produced by the patient after getting exposed to the infection. This is the key method of diagnosing and monitoring Syphilis in patients.
Some of these blood tests remain positive for the rest of the patient’s life, despite successful treatment. Other parts of the blood can change to indicate the level of activity of the Syphilis infection – this can help to monitor the success of treatments and any possible reinfection.
The Syphilis blood test is a complex test as it looks for many parameters which together gives the clinicians a more detailed picture of the infection.
(2) Syphilis Swab Test (see below)
The Syphilis swab test is a PCR test which is recommended when symptoms appear (namely, changes or breaks in the skin or mucous membranes) which are suspected to be Syphilis. This test can be carried out earlier than the blood test as Syphilis antibodies take longer to become detectable (learn more below).
A note on the difference of these tests
Both the Syphilis blood test and swab test may be recommended when dealing with patients who may be in the early stages of Syphilis. In fact, the Syphilis swab test may be positive whilst blood test is negative.
Having access to both the Syphilis swab test and blood test allows for the timely diagnosis and treatment of Syphilis, and prevents further spread of the infection to others.
Some leading authorities recommend that Syphilis and Herpes PCR on ulcer swabs should be undertaken as a matter of routine practice to prevent missing ‘atypical Syphilis’.
What does Syphilis blood test look for?
Specific Treponemal Infection:
- Treponemal IgG
- Treponemal IgM
These three are called specific treponemal tests because they only appear in the blood in patients who have Syphilis.
Syphilis TPPA and Treponemal IgG remain positive for life even after successful treatment. This is often referred to as ‘scar’ in the blood.
Non-Specific Treponemal Infection:
1. RPR (VDRL)
RPR (VDRL) are called non-specific treponemal tests because RPR can appear in the blood due to conditions other than Syphilis. However, they are useful in determining the stage of Syphilis the patient has (learn more here) and helping to monitor the treatment.
The RPR (VDRL) test is the only test that helps in diagnosing the reinfection of Syphilis (because TPPA and Treponemal IgG will remain positive for the rest of the patient’s life).
What is the window period of Syphilis?
Syphilis usually appears after 21 days post exposure.
However, the window period can range from 9 days to 90 days, for the first symptoms of primary Syphilis to appear and for the blood test of Syphilis to be positive. A negative blood test 3 months after the exposure will exclude Syphilis.
However, in about one third of patients the symptoms of primary Syphilis do not occur, and in such patients the first signs of secondary Syphilis occur a few months, sometimes upto 2 years, after getting the infection. Unfortunately in a small number of patients, a diagnosis of Syphilis is made much later, years and decades later, when the damage to heart and nervous system has already occurred.
Why are blood tests for Syphilis often repeated?
There are 4 scenarios where a blood tests for Syphilis should be repeated:
(1) After the window period
Blood tests for Syphilis become positive in most individuals 21 days after the exposure, but needs to be done at 90 days to exclude it completely.
(2) After diagnosis and treatment
In most cases, blood tests are repeated 3, 6 and 12 months after receiving treatment for Syphilis, as per existing guidelines from the professional bodies.
This is to monitor the part of the blood called RPR (or VDRL) which rises in new infections and drops with successful treatment and passage of time. When RPR (or VDRL) eventually becomes negative or stable at a particular level, it indicates that a satisfactory outcome has been achieved.
(3) In case of re-infection
The RPR (or VDRL) part of Syphilis blood test rises significantly when one gets exposed to the infection for a second time and gets reinfected. Therefore blood tests are repeated to diagnose the re-infection.
(4) During pregnancy when there is a high risk of infection
Apart from the usual antenatal checks for Syphilis at 12 weeks of pregnancy, it is recommended that Syphilis blood test is repeated at 28-32 weeks of gestation, and again at delivery.
Do I need a Syphilis test?
Test for Syphilis is recommended in the following circumstances:
- As part of routine STI tests
- After your sexual contact has been diagnosed with Syphilis
- Presence of symptoms or signs suggestive of Syphilis
- To rule out Syphilis as a work up of complex medical problems where an underlying cause has not been found
- Syphilis tests are routinely done for blood donors and as a diagnostic work up for dementia and peripheral neuropathy
- After a diagnosis of another STIs, especially gonorrhoea and HIV
- In women
- Before planning to conceive
- Before assisted fertility treatment
- Recurrent miscarriages
What do the results mean?
The Syphilis blood tests are complex and require plenty of experience and expertise in interpreting the test results and make sense of it for you. Our team has years of experience in helping patients with various stages and presentations of Syphilis.
What happens if my test is positive?
Our clinicians will assess you completely with a medical assessment, review of your sexual history and your Syphilis blood test results.
If you are tested positive for Syphilis (i.e. it is Detected) then we will discuss what it means for you, provide medication to manage the condition and ensure you don’t pass it on to your partner.
Do I have to tell my partner if I test positive?
As most cases of Syphilis in the UK are sexually transmitted a more careful assessment of your sexual history will be undertaken to ensure your suspected partners are tested.
For those who have primary Syphilis, we will look back at your partners in approx. the last 3 months. For those with early latent Syphilis, we will look back at your partners in approx. the last 2 years. In some cases the look back period can be much longer, and rarely may include all lifetime sexual partners.
Syphilis can be acquired during birth, and this possibility is considered in clinical assessment of Syphilis, even in sexually active adults. In rare cases, Syphilis test for mother is recommended where congenital Syphilis is suspected.
All of this and more will be discussed at the time of your treatment.
Syphilis PCR Swab Test
The Syphilis swab test requires a swab taken from a suspected lesion to look for Treponema Pallidum (the bacteria which causes Syphilis). A positive result will confirm the diagnosis of Syphilis.
Whilst the Syphilis blood test looks at the response of the infected person after getting the infection, the Syphilis swab test looks for the genetic material of the infective organism. Furthermore, Syphilis swab test can be positive whilst the blood test may be negative, especially very early in the course of primary Syphilis.
The lesions from which swabs are taken from can be taken in the form of cuts, erosions, ulcers and patches, which may be present on male genitalia, and in some cases from the anus, mouth and the female genitalia. Rarely such a test can also be run on biopsy specimens. PCR tests on blood samples are sometimes done as part of research studies.
Sometimes, these lesions can be due to the presence of more than one infection at the same time, for example Herpes, Syphilis and Chancroid. PCR tests from the swabs help us in making the exact diagnosis, and thus help us offer the correct treatment.
Furthermore, the swab can also be taken from lesions that are not suspected to be Syphilis to objectively rule out Syphilis.
Sample required: Swab from the lesion
Results in: 4 working days
Price: £150 (or £100 if taken with another test)
Why be treated at a specialist clinic?
However, and more importantly, we see all sorts of sexual health problems (including those referred to us by GPs) on a daily basis.
This puts us in a helpful position of being able to understand the problems you come to us with and put you on the right path in as little time as possible.
We follow guidelines set by
NICE National Institute for Health and Care Excellence
BASHH British Association for Sexual Health and HIV
BHIVA British HIV Association
FSRH Faculty of Sexual and Reproductive Healthcare
Medicine is a complicated subject and sometimes these guidelines don’t always hold the answers.
For example, treating an STI in a patient who has developed a resistance to routinely used antibiotics.
Unlike most private clinics, we have medical consultants here to help you navigate through such problems and get you on the right track in no time.
Page reviewed by Dr. Manoj Malu (Clinical Director)
Last reviewed date: 3 March 2020
Next review due: 3 March 2023
Whilst this content is written and reviewed by sexual health specialists, it is for general guidance only. It is not intended to replace the advice of your clinician.
References & Further Reading
- NHS: Syphilis – Testing
- Lab Tests Online: Syphilis Test
- Neurology Clinical Practice: Diagnostic tests for syphilis
- NICE: Syphilis
- Center for Disease Control: Syphilis in Pregnancy – 2015 STD Treatment Guidelines
- British Medical Journal: UK Sexual health clinics may be missing atypical Syphilis