C) An RPR titer of 1:16 and positive results on FTA-ABS testing is correct.

Key Concept/Objective: To know the clinical and laboratory findings of latent syphilis

Latency refers to the period after resolution of secondary disease during which there are no signs or symptoms of disease: thus, by definition, there are no clinical findings to suggest active infection. Results of serologic testing, however, will usually remain positive. Because of the immune response to the infection, levels of nontreponemal titers (e.g., RPR) typically fall to low to moderate levels (often 1:1 to 1:16). Treponemal-specific tests (e.g., FTA-ABS), which confirm the diagnosis of syphilis in people with a positive RPR, remain positive. During the first few years of latency (early latency), there is a higher chance of recurrence of the symptoms of secondary syphilis, which are typically accompanied by a rise in nontreponemal serologic titers such as RPR. A high-titer RPR (e.g., 1:256) coupled with a positive FTA-ABS would generally suggest such a recurrence of active disease. A positive RPR accompanied by a negative FTA-ABS is not consistent with latent syphilis infection but instead indicates false positivity of the RPR. In 1% to 2% of the general population, nontreponemal serologic tests may be falsely reactive; false reactive results occur more frequently in patients with collagen vascular diseases (e.g., systemic lupus erythematosus), pregnant women, and the elderly. Negative results on RPR and FTA-ABS testing suggest the absence of infection in an untreated individual.