From the Guidelines
A reactive RPR with a 1:1 titer and positive Treponema pallidum antibody indicates past or present syphilis infection.
Diagnosis of Syphilis
- The diagnosis of syphilis is typically made using a combination of nontreponemal tests (such as RPR) and treponemal tests (such as Treponema pallidum antibody) 1.
- A reactive nontreponemal test (like RPR) should be confirmed with a treponemal test to rule out false-positive results, which can occur in various medical conditions unrelated to syphilis 1.
- The presence of both a reactive RPR and a positive Treponema pallidum antibody suggests infection with Treponema pallidum, the bacterium that causes syphilis 1.
Interpretation of Test Results
- A 1:1 titer on an RPR test is considered a low titer, but in the context of a positive treponemal test, it still indicates past or present infection 1.
- Treponemal tests (like Treponema pallidum antibody) typically remain positive for life, even after treatment, while nontreponemal tests (like RPR) may become nonreactive after treatment 1.
- It's essential to note that HIV infection may not affect the performance of standard syphilis tests, but false-positive nontreponemal serologic tests might be more common in HIV-infected individuals 1.
From the Research
Interpretation of Reactive RPR and Treponema pallidum Antibody Results
- A reactive RPR (Rapid Plasma Reagin) with a 1:1 titer and positive Treponema pallidum antibody indicates a possible syphilis infection, but the results should be interpreted with caution 2, 3, 4, 5, 6.
- The RPR test is a non-treponemal test that detects antibodies against the syphilis bacterium, while the Treponema pallidum antibody test is a treponemal test that detects specific antibodies against the bacterium 3, 4.
- A low RPR titer (1:1) may indicate a false-positive result or a very early stage of syphilis infection 6.
- The presence of Treponema pallidum antibody suggests a current or past syphilis infection, but it does not distinguish between the two 3, 4.
- Further testing, such as a confirmatory treponemal test (e.g., TP-EIA or TP-PA), may be necessary to confirm the diagnosis of syphilis 2, 5.
Clinical Implications
- The results of the RPR and Treponema pallidum antibody tests should be interpreted in the context of the patient's clinical presentation, medical history, and risk factors for syphilis 5, 6.
- A healthcare provider may consider ordering additional tests, such as a lumbar puncture or a cerebrospinal fluid analysis, to rule out neurosyphilis or other complications of syphilis 5.
- Patients with a reactive RPR and positive Treponema pallidum antibody should receive prompt treatment with antibiotics, regardless of the stage of the infection 6.