RPR is a non-specific serological test for syphilis spirochetes, like TRUST (toluidineredunheatedserumtest). After a certain period of infection with syphilis spirochetes, a certain number of cardiolipin antibodies are produced in the serum, and this test is used to determine the titer of these antibodies by immunological methods to guide diagnosis and treatment. In terms of diagnosis, TPHA and TPPA are specific syphilis spirochete antigen serologic tests, and are only diagnostic if both TPHA (or TPPA) and RPR (or TRUST) are positive; patients with a positive TPHA (or TPPA) should be further tested for RPR or TRUST. The RPR (or TRUST) titer is related to the activity of syphilis and is a common indicator for clinical evaluation of syphilis treatment effect. After regular syphilis treatment, a decrease in serum RPR (or TRUST) titer or even a change from positive to negative indicates effective treatment, but regular review is still needed to avoid recurrence and reinfection. False negative RPR is common in patients with stage I syphilis (less than 2-3 weeks of infection), so suspected patients should be rechecked after 4 weeks. false negative RPR can also be seen in patients with immediate treatment of syphilis infection, a few patients with advanced syphilis, or for other reasons such as pre-banding phenomenon (due to excessive amount of anticardiolipin antibodies in the serum inhibiting the appearance of a positive reaction), testing technology or reagent quality.