Which test is less likely to be reactive in primary and early secondary syphilis?

The MHA-TP (Microhemagglutination assay for Treponema pallidum) test is a treponemal test that detects antibodies against Treponema pallidum, the bacterium that causes syphilis. This test is generally more specific and is used primarily in the confirmation of syphilis after a non-treponemal test, such as RPR or VDRL, has yielded a positive result.

In the case of primary and early secondary syphilis, non-treponemal tests like RPR and VDRL might yield positive results, but they are often not as sensitive in the very early stages of the infection. Consequently, the period of time in which antibodies are being produced can result in the MHA-TP test being less reactive compared to these non-treponemal tests, which can show reactivity in the initial phases of syphilis.

Darkfield microscopy is frequently employed during the primary stage to directly visualize the spirochetes in lesions, therefore, it does not assess antibody response but rather detects the organism directly.

Overall, MHA-TP is less likely to be reactive in primary and early secondary syphilis due to the timing of antibody