In syphilis serology, a nonreactive RPR with a reactive FTA-ABS most commonly indicates which stage or history?

In syphilis serology, a nonreactive RPR with a reactive FTA-ABS most commonly indicates which stage or history?

• A. Primary infection
• B. Past infection
• C. Active infection
• D. False positive

Answer: (B)

The key idea is how the two types of syphilis tests behave over time. Non-treponemal tests like RPR track disease activity and tend to become nonreactive after the infection is treated or in late, inactive infection. Treponemal tests like FTA-ABS detect antibodies to the bacterium and usually remain positive for life, even after treatment. So, if the RPR is nonreactive but the FTA-ABS is reactive, it points to a history of syphilis that has been treated. The treponemal antibodies persist, indicating past infection, while the non-treponemal antibodies have waned, reflecting no active disease at present.

The key idea is how the two types of syphilis tests behave over time. Non-treponemal tests like RPR track disease activity and tend to become nonreactive after the infection is treated or in late, inactive infection. Treponemal tests like FTA-ABS detect antibodies to the bacterium and usually remain positive for life, even after treatment.

So, if the RPR is nonreactive but the FTA-ABS is reactive, it points to a history of syphilis that has been treated. The treponemal antibodies persist, indicating past infection, while the non-treponemal antibodies have waned, reflecting no active disease at present.