Syphilis Antibody Testing

An instant syphilis test uses a small blood sample, usually taken with a finger prick, to detect antibodies to syphilis. Results are typically available within around 30 minutes.

Before the test, you will be asked about your symptoms, sexual history, and any recent exposure. If you have symptoms such as a painless sore or rash, a physical examination may also be recommended as part of your assessment.

If very early syphilis is suspected, particularly if you have a chancre or other suitable infectious lesion, an initial antibody test may be negative because antibodies may not yet be detectable. In this situation, a healthcare professional may recommend additional testing, such as direct testing of the lesion using PCR for Treponema pallidum DNA where available, and/or repeat serology.

No special preparation is needed before an instant syphilis test. You can eat and drink as normal.

If you are having a broader STI screen, you may be asked to avoid passing urine for around two hours before your appointment in case a urine sample is needed. If you require a certificate of your results, bring a valid photo ID.

It is also important to consider the timing of your last possible exposure. An instant syphilis test has a window period, so testing too soon may not detect a recent infection. If you are unsure when to test, your clinician can advise you.

The window period for an instant syphilis test is up to 12 weeks after exposure. A result at 12 weeks is considered conclusive for most people.

Some infections may be detected as early as 3 to 6 weeks, but testing during this time may not identify every infection. If you have symptoms such as a painless sore or rash, you should be assessed as soon as possible, even if you are still within the window period.

The instant syphilis test is a rapid antibody test that detects antibodies your immune system produces in response to the bacteria that cause syphilis.

A small blood sample is applied to a test device containing syphilis antigens. If syphilis antibodies are present, they bind to these antigens and produce a visible result, usually within 30 minutes. Because the test detects antibodies rather than the bacteria itself, it may not identify very recent infections.

Instant syphilis tests can provide useful results, but their accuracy varies depending on the specific test used and the stage of infection. Tests may be less sensitive during very early syphilis, when antibodies may not yet be detectable.

A reactive instant antibody test does not by itself establish whether the infection is current, previous or adequately treated. Further laboratory testing, including confirmatory treponemal testing and a quantitative RPR or VDRL test, may be required to interpret the result and guide clinical management.

A negative result also cannot completely exclude very early syphilis, particularly if you have symptoms or have recently been exposed. If early syphilis is suspected, your healthcare professional may recommend repeat serology and/or direct testing of an appropriate lesion where available.

Because treponemal antibodies usually remain detectable for many years and often for life after infection, an antibody test may remain reactive even after successful treatment.

If you have symptoms suggestive of syphilis, a known sexual contact with syphilis, or another significant reason to suspect infection, you should seek clinical assessment promptly rather than waiting for a specific window period.

Testing may be performed at the time of assessment, although an early negative result may not exclude recent infection. BASHH recommends repeat screening three months after a high-risk contact because negative results within three months of infection cannot exclude early syphilis. If a possible chancre is present and initial testing is negative, your healthcare professional may recommend earlier repeat testing and/or direct testing of the lesion.

If you have no symptoms but are concerned about a recent exposure, speak with a healthcare professional about the most appropriate timing for testing based on when the exposure occurred.

Syphilis testing may be recommended depending on your symptoms, sexual history, exposure risk and clinical circumstances. This may include:

• As part of an STI screening assessment based on your individual risk
• Following sexual contact with someone diagnosed with syphilis
• If you have symptoms or signs that could be caused by syphilis
• If your healthcare professional considers syphilis as part of the assessment of an unexplained medical condition or neurological, eye or ear symptoms
• During pregnancy as part of routine antenatal screening
• If you have another STI or circumstances that indicate an increased risk of syphilis

People who have previously had syphilis may also require testing if reinfection is suspected.

In people who are pregnant, syphilis screening is routinely offered during antenatal care. Additional testing later in pregnancy may be offered when there is an identified risk of infection or reinfection.

Your healthcare professional can advise whether syphilis testing is appropriate based on your individual circumstances.

There are several reasons why syphilis blood tests may need to be repeated:

(1) After a recent exposure or when early infection is suspected

Syphilis antibodies may not be detectable in the very early stages of infection. BASHH advises that negative results within three months of infection cannot exclude early syphilis. If you have symptoms such as a possible chancre, repeat serology may be recommended, and direct testing of a suitable lesion may also be considered.

(2) After diagnosis and treatment

Follow-up blood tests are used to assess the response to treatment and identify possible reinfection or treatment failure. BASHH recommends clinical and serological follow-up, including quantitative RPR testing, with follow-up at 3, 6 and 12 months, and further six-monthly testing when indicated. The exact follow-up schedule can vary depending on the stage of syphilis, treatment, clinical circumstances and risk of reinfection.

The RPR or VDRL titre is assessed by looking at changes over time. A four-fold change in titre is clinically significant when assessing treatment response or possible reinfection. The test does not necessarily become negative after successful treatment, and some people remain “serofast” with a persistent low-level titre.

(3) If reinfection is suspected

A significant rise in the RPR titre, particularly a sustained four-fold or greater increase compared with a previous result, can suggest reinfection or treatment failure. Clinical symptoms and the possibility of a new exposure are also taken into account when interpreting the results.

(4) During pregnancy

All pregnant people should be offered syphilis screening at their first antenatal visit. Additional testing later in pregnancy should be offered when there is a recognised risk of syphilis or reinfection, rather than using a universal 28–32 week and delivery schedule for everyone. Serology may also be performed at delivery in some circumstances, particularly where there is concern about reinfection or to assist with assessment for congenital syphilis.

A physical examination is not usually needed if you have no symptoms and are attending for routine testing.

If you have symptoms such as a painless sore, rash, or swollen lymph nodes, your clinician may recommend an examination alongside the blood test to help make an accurate diagnosis.

There are different types of laboratory tests that may be used to diagnose syphilis, depending on your symptoms, stage of infection and clinical circumstances.

(1) Syphilis Blood Tests

Syphilis blood testing generally involves two types of serological tests:

• Treponemal tests, which detect antibodies directed against Treponema pallidum. These usually remain reactive for many years and often for life, even after successful treatment.
• Non-treponemal tests, such as RPR or VDRL, which measure antibody titres. These are used alongside clinical history and other test results to help assess infection and monitor the response to treatment or identify possible reinfection.

Because these tests provide different information, they are interpreted together rather than as a single measure of whether the infection is simply “active” or “inactive.”

(2) Syphilis Lesion Swab / PCR

If you have a suitable infectious lesion, such as a chancre or other mucocutaneous lesion that may be caused by syphilis, a sample may be collected for direct testing. PCR can detect Treponema pallidum DNA in a lesion and can be particularly useful when early syphilis is suspected.

Lesion PCR can sometimes detect infection before syphilis antibodies have become detectable in the blood, meaning that a person with very early syphilis may have a positive lesion PCR while their blood test is still negative.

A note on the difference between these tests

Blood testing and lesion PCR provide different types of information and may both be appropriate in suspected early syphilis. A negative blood test does not necessarily exclude very early infection, particularly when a suspicious lesion is present.

The choice of testing depends on your symptoms, examination findings, timing of possible exposure, previous syphilis infection and treatment history. Your healthcare professional can advise which tests are appropriate.

Where anogenital or oral ulcers are present, clinicians may consider testing for syphilis alongside other possible causes, such as herpes, based on the clinical presentation and local testing protocols.

You can receive your test results by either text or email.

Results are generally reported as REACTIVE or NON-REACTIVE.

• NON-REACTIVE: No syphilis antibodies were detected. However, very early infection may not yet be detectable, so repeat or additional testing may be recommended if you have recent exposure or symptoms.

• REACTIVE: Syphilis antibodies were detected. This does not by itself distinguish a current infection from a previous treated infection. Further laboratory testing, including treponemal and quantitative RPR/VDRL testing, may be needed alongside clinical assessment.

If the test is invalid or inconclusive, a repeat sample may be required.

Yes. Until you receive your result, it is best to avoid vaginal, oral, and anal sex, particularly if you have symptoms such as a painless sore or rash.

If your test is positive, your clinician will explain when it is safe to resume sexual activity after treatment. If you have an active sore, avoid direct contact with it and do not share items that may come into contact with the affected area, such as towels.

If your instant syphilis test is reactive, further laboratory testing and clinical assessment are usually needed. This may include confirmatory treponemal testing and a quantitative RPR or VDRL test to help determine whether the infection is current or previously treated and establish a baseline for monitoring treatment.

If syphilis is confirmed, your clinician will recommend the appropriate antibiotic treatment and follow-up.

You should avoid sexual contact until at least two weeks after you and your partner(s) have completed treatment, or until any infectious lesions have healed, whichever is later, unless your clinician advises otherwise.

If syphilis is confirmed, it is important to inform relevant recent sexual partners so they can receive appropriate assessment and treatment.

The partners who need to be contacted and the relevant exposure period depend on the stage of syphilis and when the infection was acquired. A reactive rapid test should first undergo appropriate laboratory testing and clinical assessment.

If you do not feel comfortable contacting partners yourself, healthcare professionals can usually provide confidential partner-notification support.

Yes. A certificate of your instant syphilis test results can be provided if you need one for purposes such as employment or travel.

You will usually need to provide a valid photo ID, such as a passport or driving licence, so your identity can be verified before the certificate is issued. Results are typically available within 30 minutes, so the certificate can usually be prepared during your appointment.