From the Guidelines
A non-reactive Rapid Plasma Reagin (RPR) test result means that the individual likely does not have syphilis, as the test did not detect antibodies produced in response to syphilis infection. The RPR test is a nontreponemal test that detects antibodies against the bacteria that causes syphilis (Treponema pallidum) 1. A non-reactive result suggests that the individual has not been exposed to or infected with the bacteria. However, it's essential to consider the following:
- There can be false negatives early in infection, so retesting may be recommended if exposure is suspected.
- The RPR test remains reactive in most people even after successful treatment, so a non-reactive result also suggests no history of syphilis.
- For definitive diagnosis, especially in low-risk populations, a more specific treponemal test (like FTA-ABS or TPPA) may be used to confirm results, as nontreponemal tests like RPR can occasionally produce false-positive results due to various medical conditions 1. If syphilis was a concern, this non-reactive result is generally reassuring, but always discuss the full interpretation and any need for follow-up with your healthcare provider, particularly in high-risk populations or during pregnancy, where screening and treatment guidelines are more stringent 1.
From the Research
Non-Reactive Rapid Plasma Reagin (RPR) Test Result
A non-reactive RPR test result indicates that the test did not detect the presence of syphilis antibodies in the blood. However, this result should be interpreted with caution, as it does not necessarily rule out the possibility of syphilis infection.
Limitations of RPR Test
- The RPR test is non-specific and can produce false-positive results, especially in patients with hepatitis C virus (HCV) infection 2.
- The test can also produce false-negative results, particularly in primary and late latent syphilis cases 3, 4.
- The RPR test is slow to change and variable in its rate of decline post-treatment, making it a poor test for assessing the adequacy of treatment or diagnosing re-infection 5.
Characteristics of Non-Reactive RPR Test Results
- Age >35 years is an independent factor associated with non-reactive RPR results in primary syphilis cases 3.
- Male gender, Caucasian ethnicity, and diagnosis during a syphilis outbreak period are associated with non-reactive RPR results in primary syphilis cases 4.
- Male gender, Canadian Aboriginal, Caucasian, and black ethnicity are associated with non-reactive RPR results in late latent syphilis cases 4.
Clinical Implications
- RPR testing alone is insufficient to diagnose primary and late latent infections, especially in middle-aged and elderly individuals 3, 4.
- The slow decay in RPR titres post-therapy and the inability of a significant number of subjects to achieve a non-reactive result over time makes RPR a poor test for assessing the adequacy of treatment or in diagnosing re-infection 5.