Diagnosis of Syphilis

Syphilis is not an easy disease to diagnose by using only clinical symptoms and signs.  This is because there are so many ways syphilis can present.  Syphilis is a complex infection with many different stages.  There are still many studies being done to understand the infection and disease process.

    Blood tests

    Blood tests are the most common way in which syphilis is diagnosed

  • Blood
  • Blood tests are the most common way in which syphilis is diagnosed.  Blood cannot differentiate the different stages of syphilis infection.  Screening blood tests for syphilis are RPR (rapid plasma reagin) and VDRL (venereal disease research laboratory).  These blood tests sometimes show false positive results which means they are positive even when the person does not have syphilis.  For this reason, blood tests which are VDRL or RPR positive should be confirmed with a TPHA (treponemalpallidum particle agglutination) or FTA-Abs (fluorescent treponemal antibody absorption test).  TPHA and FTA-Abs blood tests are more expensive but also more accurate than VDRL and RPR tests.  Occasionally, TPHA and FTA-Abs blood tests may also be false positive when the patient has a condition like varicella (chicken-pox virus), measles, lymphoma, malaria, tuberculosis or even pregnancy.

  • Finger prick screening test
  • A rapid screening test is performed similarly to a glucose finger prick test.  A small prick is made in a finger to obtain a drop of blood.  This is then smeared on a special rapid diagnostic kit.  An RPR result can be available within 5 minutes from performing this test.  All positive results will still need a formal blood test to confirm the diagnosis.

  • Microscopy
  • A swab from fluid from a syphilitic chancre may reveal the bacterium when using microscopy.  This test is not done often as it is easier and more convenient to draw blood. Microscopy needs to be done within 10 minutes of obtaining the fluid from the chancre which is not always possible.  Microscopy is also not able to differentiate between the different stages of syphilis.

    lumbar puncture

    If the patient has symptomsof neurosyphilis, a lumbar puncture may be performed

  • Lumbar puncture
  • Neurosyphilis is tricky to diagnose.  If the patient has symptoms which are suspicious of neurosyphilis and they have a positive blood test for syphilis, a lumbar puncture may be performed.  If neurosyphilis is present the cerebral spinal fluid results of the lumbar puncture would generally show a high leukocyte and protein count.  Neurosyphilis is officially diagnosed when a treponema pallidum particle agglutination test is positive for syphilis on the cerebral spinal fluid.