Syphilis Antibody(Syphilis Ab) Determination Kit (Fluorescence Immunochromatographic Assay) is an in vitro diagnostic test kit. Syphilis is caused by the intracellular Gram-negative spirochete bacterium Treponema pallidum subspecies pallidum. The only way to definitively diagnose syphilis is through testing, which can help diagnose syphilis in its earliest stages, when it is easiest to treat.