From the Guidelines
To check if a patient has active or treated syphilis, order a two-step testing approach: first, a nontreponemal test such as RPR (Rapid Plasma Reagin) or VDRL (Venereal Disease Research Laboratory), followed by a treponemal-specific test like TP-PA (Treponema pallidum particle agglutination) or FTA-ABS (fluorescent treponemal antibody absorption) for confirmation, as recommended by the most recent guidelines 1. This approach is based on the understanding that nontreponemal tests provide quantitative titers that help determine disease activity and treatment response, while treponemal tests usually remain positive for life regardless of treatment 2. Some key points to consider when interpreting the results include:
- A positive treponemal test with a negative nontreponemal test typically indicates previously treated or very early/late syphilis 1.
- Nontreponemal test titers should decline after successful treatment (4-fold decrease within 6-12 months) 2.
- Treponemal tests usually remain positive for life regardless of treatment 2.
- Clinical correlation with the patient's history, physical examination findings, and risk factors is essential for proper interpretation of these results. It's also important to note that some labs now use the reverse sequence algorithm, starting with treponemal tests, and then retesting reactive results with a non-treponemal test to confirm diagnosis 1. For patients with suspected neurosyphilis, a lumbar puncture for CSF analysis (VDRL, cell count, protein) may be necessary. Overall, the two-step testing approach provides a comprehensive assessment of syphilis infection and treatment status, and is supported by the most recent guidelines 1.
From the FDA Drug Label
In venereal disease, when co-existent syphilis is suspected, dark field examinations should be done before treatment is started and the blood serology repeated monthly for at least 4 months. To check if a patient has active or treated syphilis, blood serology tests should be ordered, and if possible, dark field examinations should be performed. These tests should be repeated monthly for at least 4 months to monitor the patient's condition 3.
From the Research
Diagnostic Tests for Syphilis
To determine if a patient has active or treated syphilis, several diagnostic tests can be ordered. These include:
- Venereal Disease Research Laboratory (VDRL) test
- Rapid Plasma Reagin (RPR) test
- Treponema pallidum particle agglutination (TP-PA) test
- Fluorescent treponemal antibody absorption (FTA-Abs) test
Test Sensitivities
The sensitivities of these tests vary:
- The sensitivity of the VDRL test confirmed by TP-PA is 71% 4
- The sensitivity of the TP-PA test as the first-line diagnostic test is 86% 4
- The sensitivity of the RPR test is similar to that of the VDRL test, with a sensitivity of 75% for neurosyphilis diagnosis 5
- The sensitivity of the CSF-RPR and CSF-RPR-V tests is lower than that of the CSF-VDRL, with sensitivities of 56.4% and 59.0% for laboratory-diagnosed neurosyphilis, respectively 6
Test Specificities
The specificities of these tests also vary:
- The specificity of the VDRL test for current neurosyphilis is 99% 5
- The specificity of the RPR test for current neurosyphilis is 99.3% 5
- The specificity of the TP-PA test is not explicitly stated in the provided studies, but it is considered a highly specific test for syphilis diagnosis
Choosing the Right Test
When choosing a diagnostic test for syphilis, it is essential to consider the stage of the disease and the patient's clinical presentation. The VDRL test is commonly used for screening, while the TP-PA test is more sensitive and specific for diagnosing primary syphilis 4. The RPR test can be used as an alternative to the VDRL test in some cases, but its sensitivity and specificity may vary depending on the population being tested 5, 6.