RPR: non reactive; FTA-ABS: reactive — what is the most likely interpretation?

RPR: non reactive; FTA-ABS: reactive — what is the most likely interpretation?

• A. Past infection
• B. Current active infection
• C. Early syphilis
• D. False positive

Answer: (A)

The key idea is how these tests behave over the course of syphilis infection and after treatment. Treponemal tests (like FTA-ABS) stay positive for life once someone has been exposed to Treponema pallidum, even if the infection has been cleared. Non-treponemal tests (like RPR) are more variable: they tend to become nonreactive after successful treatment and may drop in active infection as the disease is treated or as time passes. So when FTA-ABS is reactive but RPR is nonreactive, it most strongly points to a past infection that has been treated. The person had syphilis at some point, treatment resolved the active infection, and the treponemal antibodies remain detectable long-term. While early infection can sometimes show discordant results, the pattern described most commonly reflects a remote, not currently active, infection. False positives are unlikely with FTA-ABS in this combination, making past infection the best interpretation.

The key idea is how these tests behave over the course of syphilis infection and after treatment. Treponemal tests (like FTA-ABS) stay positive for life once someone has been exposed to Treponema pallidum, even if the infection has been cleared. Non-treponemal tests (like RPR) are more variable: they tend to become nonreactive after successful treatment and may drop in active infection as the disease is treated or as time passes.

So when FTA-ABS is reactive but RPR is nonreactive, it most strongly points to a past infection that has been treated. The person had syphilis at some point, treatment resolved the active infection, and the treponemal antibodies remain detectable long-term. While early infection can sometimes show discordant results, the pattern described most commonly reflects a remote, not currently active, infection. False positives are unlikely with FTA-ABS in this combination, making past infection the best interpretation.