Syphilis Diagnosis

Syphilis needs early detection for effective cure and prevention of transmission to sexual partners and unborn babies (among pregnant mothers). Persons suspecting syphilis or those indulging high risk sexual behaviors can visit a genitourinary (GUM) clinic, sexual health clinic or their general practitioners for detection and diagnosis. The earlier syphilis is treated, the less chance there is of serious complications.

Diagnosis comprises of the following steps:

Physical examination

The patient is physically examined. For men the penis, foreskin and urethra and for women internal examination of the vagina and external examination of the vulva is important.

For both men and women, mouth, tongue, anus and rectum is examined. In primary syphilis this may show a painless sore or chancre.

Blood tests

Those who are infected with syphilis have presence of antibodies against the syphilis bacteria. This can be detected in blood.

A positive result indicates presence of these antibodies and means that the person either has the infection or had it earlier. The antibodies can remain in blood for years, even after a previous infection was successfully treated.

A negative result does not necessarily mean that the person does not have syphilis as the antibodies may not be detectable for up to three months after infection. The test may be repeated in three months.

Blood tests are also recommended for pregnant women in order to detect the risk to the unborn baby and treat the mother accordingly. The blood test is usually done during an antenatal appointment at weeks 11-20 of pregnancy. If the test is positive, treatment for both the mother and baby can be started.

Blood tests include the Treponemal enzyme immunoassay (EIA). This can detect the immunoglobulin M (IgM) for early infection or immunoglobulin G (IgG) (the latter becomes positive at 5 weeks) or both. Both are checked for screening. This is the most important test for primary syphilis detection.

Other tests of blood samples include:

  • T. pallidum chemiluminescent assay
  • T. pallidum haemagglutination assay (TPHA)
  • T. pallidum particle agglutination assay (TPPA)
  • Fluorescent treponemal antibody absorbed test (FTA-abs)
  • T. pallidum recombinant antigen line immunoassay

All of these will be positive in secondary and early latent syphilis.

Venereal disease reference laboratory (VDRL) or rapid plasmin reagin (RPR)  or a quantitative VDRL can be used as an indication of the stage of syphilis and is also used for monitoring treatment.


From the chancre, or the sore, a swab (using a sterile cotton bud) is used to take a small sample of fluid. This is then fixed onto a glass slide and stained with special dyes. Then the slide is looked under the microscope in the clinic or sent to a laboratory for examination. The technique is called Dark field microscopy.

For detection samples from the lymph nodes in early syphilis may be taken. Other tests to seen the bacteria directly include Direct fluorescent antibody (DFA) test and Polymerase chain reaction (PCR).

Tests for other sexually transmitted infections

Those with syphilis are at risk of other sexually transmitted infections like HIV, chlamydia and gonorrhoea. Tests for these is important during diagnosis of syphilis.

Lumbar puncture

Those with tertiary syphilis or infection of the brain and nerves need examination of the Cerebrospinal fluid or CSF. This is done by lumbar puncture.

ECG and Echocardiography

Those with tertiary syphilis or infection of the heart need an ECG and Echocardiography for diagnosis of the extent of damage.

Further Reading

Last Updated: Jun 21, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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