This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'Which of the following is the most sensitive test for Treponema? \nSelect and explain. \nA. VDRL, B. RPR, C. FTA-ABS, D. Kahn', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Treponemal tests detect antibody specific to T pallidum, such as an indirect immunofluorescent procedure called the fluorescent treponemal antibody (FTA-ABS), which uses spirochetes fixed to slides. ABS refers to an absorption step that removes nonspecific anti spirochetal antibodies often found in normal serum. FTA-ABS is the most sensitive test in all stages of syphilis, and is the best confirmatory test for a serum reactive to a screen such as RPR or VDRL. FTA-ABS antibodies rise more quickly in primary syphilis and remain positive in teiary syphilis. In late syphilis, approximately 1/3 of these patients may have a nonreactive VDRL or RPR. Therefore, if there is clinical suspicion of late syphilis and the VDRL or RPR is nonreactive, the FTA-ABS should be performed. This test is both sensitive and specific for syphilis infection. Less than 1% false positives are due to SLE, RA or old-age. All 1+ or minimally reactive results are considered equivocal; in the absence of historical or clinical evidence of treponemal infection, a second specimen should be submitted for serological testing. Ref: Ray C.G., Ryan K.J. (2010). Chapter 37. Spirochetes. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.', 'role': 'assistant'}]