Which test is considered the most sensitive in detecting primary syphilis?

The test that is considered the most sensitive in detecting primary syphilis is the FTA-ABS (Fluorescent Treponemal Antibody Absorption) test. This test specifically detects antibodies that are produced in response to Treponema pallidum, the bacterium that causes syphilis.

In the context of primary syphilis, where the infection is newly acquired and the patient may only exhibit the characteristic chancre, the FTA-ABS test can provide definitive evidence of infection much earlier than non-treponemal tests. Unlike non-treponemal tests (such as RPR and VDRL), which may not become reactive immediately after infection, the FTA-ABS test remains consistently positive once antibodies are present, making it particularly valuable for confirming a diagnosis in the initial stages of the disease.

The MHA-TP (Microhemagglutination Test for Treponema Pallidum) is also a specific treponemal test but is less commonly used than the FTA-ABS in clinical practice. While its sensitivity is comparable, it typically requires more complex methodology. Thus, for the detection of primary syphilis, FTA-ABS is favored for its high sensitivity