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Which blood tests are commonly used to screen for syphilis?

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Scanning electron micrograph of Treponema pallidum, the spirochete bacterium that is the causative agent of syphilis. — syphilis Scanning electron micrograph of *Treponema pallidum*, the spirochete bacterium that is the causative agent of syphilis.

Laboratory screening for syphilis primarily involves serological tests performed on blood serum. These are categorized into two main types:12

Nontreponemal Tests

These tests detect reagin, an antibody-like substance produced in response to the infection. Common examples include:12
* Rapid Plasma Reagin (RPR) test12
* Venereal Disease Research Laboratory (VDRL) test12

Because these tests are not fully specific to syphilis and can yield "false positive" results due to other infections, positive findings are typically followed by more specific testing.12

Treponemal Tests

These tests detect antibodies that specifically target Treponema pallidum, the bacterium that causes the disease. Common examples include:1
* T. pallidum particle agglutination assay (TPPA) or hemagglutination assay (TPHA)1
* Enzyme immunoassay (EIA)1
* Fluorescent treponemal antibody absorption (FTA-ABS) test1

In clinical practice, a diagnosis is most often confirmed by using both a nontreponemal and a treponemal test.1