Test for Syphilis
There are 4 different tests for syphilis.
In general, they should be done in combination to determine the presence of infection and whether the infection is new or old. The earliest time to have test for syphilis is at least 2 weeks after at-risk exposure.
1. Treponema Pallidum (TP) antibody Test
This tests for the presence of antibody IgM and IgG in blood.
IgM is usually developed from 2 weeks after infection by Treponema Pallidum. Therefore this test can detect early infection by Treponema Pallidum.
IgG is usually produced by the body about 4 weeks after contact with the infection and remains positive for life even after treatment. Therefore, it is used to determine infection over 4 weeks or previous infection of syphilis. This test us usually used as a screening test for syphilis.
2. VDRL Test
VDRL is a secondary test for syphilis which provides a semi-quantitative level of antibody in blood. It is used as a confirmation if TP antibody is positive, determine the likely stage of infection and response to treatment. If positive, conventionally it is reported as "reactive" instead of positive and a negative result is reported as "non-reactive". In a positive result, a level is also given as 1:2, 1:4, 1:8...1:32 etc. The higher the second number indicts the level of dilution that the test remains positive, ie higher number indicates high concentration of antibody and more advanced infection. After treatment, the level will reduce and it can take up to 6-12 months for the test to become "non-reactive" again. In some cases, the report may show "NEAT" which indicates the test is only positive in an undiluted sample which may still indicate treated syphilis.
3. FTA antibody and TPHA Test
FTA and TPHA are confirmation tests to verify a positive TP antibody test. These 2 tests will always remain positive after infection of Treponema Pallidum. However, these two tests are subjected to higher technician variability, therefore they are usually not used as first line tests.