Test Overview

Syphilis tests detect antibodies to the bacterium that causes syphilis (Treponema pallidum) in blood, body fluid, or tissue. The tests are used to screen for or to confirm a syphilis infection.

Syphilis is a sexually transmitted disease (STD) that is usually spread during sexual contact, including kissing or oral sex.

Tests used to screen for syphilis include:

• Venereal disease research laboratory (VDRL) test. The VDRL test checks for an antibody that can be produced in people who have syphilis. This antibody is not produced as a reaction to the syphilis bacteria specifically, so this test is sometimes not accurate. The VDRL test may be done on a sample of blood or spinal fluid. The VDRL test is not very useful for detecting syphilis in very early or advanced stages.
• Rapid plasma reagin (RPR) test. The RPR test also detects syphilis antibodies.
• Enzyme immunoassay (EIA) test. This is a newer blood test that check for antibodies to the bacteria that cause syphilis. A positive EIA test should be confirmed with either the VDRL or RPR tests.

Tests used to diagnose syphilis include:

• Fluorescent treponemal antibody absorption (FTA-ABS) test. The FTA-ABS test detects antibodies to the bacteria that cause syphilis and can be used to detect syphilis except during the first 3 to 4 weeks after exposure to syphilis bacteria. It is more difficult to do and may be used to confirm a syphilis infection after another method tests positive for the syphilis bacteria. The test can be done on a sample of blood or spinal fluid.
• Treponema pallidum particle agglutination assay (TPPA). The TPPA test is used to confirm a syphilis infection after another method tests positive for the syphilis bacteria. This test detects antibodies to the bacteria that cause syphilis and can be used to detect syphilis in all stages, except during the first 3 to 4 weeks. This test is not done on spinal fluid.
• Darkfield microscopy. This test uses a special microscope to examine a sample of fluid or tissue from an open sore (chancre) for the syphilis bacteria. If syphilis is present, it can be seen as corkscrew-shaped objects on the microscope slide. This test is used mainly to diagnose syphilis in an early stage.
• Microhemagglutination assay (MHA-TP). The MHA-TP is used to confirm a syphilis infection after another method tests positive for the syphilis bacteria. The MHA-TP test detects antibodies to the bacteria that cause syphilis and can be used to detect syphilis in all stages, except during the first 3 to 4 weeks. This test is not done on spinal fluid. The MHA-TP test is rarely used any more.