Background The usefulness of syphilis rapid tests in STI counselling services is under discussion in Germany. For this reason, we evaluated the performance of the Determine® Syphilis rapid test (TP-RT) in comparison to standard serological syphilis tests.
Materials and Methods The TP-RT was carried out in 2,203 serum or plasma samples from the German syphilis consiliary laboratory (Labor Krone GbR, Bad Salzuflen) representing a broad spectrum of relevant samples from public health institutions, STI and HIV ambulances, hospitals and others, including samples from 532 MSM, 417 female sex workers and 260 pregnant women. The treponemal antibody status was determined using the Architect® Syphilis TP CMIA (Abbott) as a screening test.
Results The TP-RT specificity was determined at 99.4% and the sensitivity at 97.0%. For 12.2% of the positive sera the TP-RT demonstrated only borderline findings. From a subset of 135 positive samples the TP-RT showed reactivity after 15 min in 121 (89.7%), 30 min in 129 (95.6%), 60 min in 131 (97.0%) and after 24 h in all of 135 (100%). More than 70% of the positive findings were related to past treponemal infections. In two cases of primary syphilis a borderline TP-RT result only occurred after 45 to 60 min.
Discussion The TP-RT is not able to differentiate active from past treponemal infections. Any reactive TP-RT finding has to be further tested by conventional syphilis tests. Negative TP-RT results after a reading time from 15 to 30 minutes does not exclude the presence of highly infectious early stages of syphilis. A minimum reading time of 1–2 hours is recommended. The high number of borderline findings even in active syphilis cases poses the risk of incorrect assessment of the test results. The routine use of rapid tests is not recommended for syphilis diagnosis in Germany.
- Rapid test
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