The Rapid Plasma Reagin (RPR) test is a common screening tool used to detect syphilis, a bacterial infection. However, a “false positive” RPR result can occur, meaning the test indicates syphilis is present when it is not. A false positive RPR result does not signify an active syphilis infection.
Understanding the RPR Test
The RPR test is a nontreponemal test to identify antibodies produced by the body in response to tissue damage caused by syphilis. These antibodies, called reagins, are not specific to the Treponema pallidum bacteria. Instead, they react to lipoidal antigens, which are substances like cardiolipin, lecithin, and cholesterol, released from damaged host cells during an infection. Its non-specificity means other conditions can also trigger these antibodies.
Medical Conditions Causing False Positives
Various medical conditions and physiological states can lead to a false positive RPR test result. These conditions cause the body to produce antibodies that mistakenly react with the RPR test’s antigens, even without the presence of syphilis.
Autoimmune diseases are a notable category contributing to false positive RPR results. Conditions such as systemic lupus erythematosus (SLE), rheumatoid arthritis, and antiphospholipid syndrome can induce the production of antibodies that cross-react with the RPR test components.
Acute and chronic infections beyond syphilis are frequent causes of false positives. These include viral infections like mononucleosis, hepatitis C, and HIV. Bacterial infections such as Lyme disease, pneumonia, tuberculosis, and rickettsial diseases like typhus or Rocky Mountain spotted fever can also trigger a false positive RPR. Malaria and leprosy are further examples of infections known to cause these non-specific antibody reactions.
Other factors, distinct from active infections or autoimmune disorders, can also result in a false positive RPR. Pregnancy is a common physiological state that can lead to a false positive result. Recent vaccinations, including those for COVID-19, have also been observed to cause transient false positives. Additionally, intravenous drug use, chronic liver disease, and older age are recognized factors that may contribute to a false positive RPR test.
Next Steps After a False Positive Result
Receiving a positive RPR test necessitates further investigation. The RPR test is a screening tool, and its positive result must be followed by more specific testing to confirm or rule out a syphilis infection. This confirmatory step helps distinguish a true syphilis infection from a false positive reaction caused by other conditions.
Confirmatory tests, treponemal tests, specifically detect antibodies against Treponema pallidum, the bacterium responsible for syphilis. Examples of these tests include the Fluorescent Treponemal Antibody Absorption (FTA-ABS) test, Treponema pallidum Particle Agglutination (TP-PA) assay, Enzyme Immunoassay (EIA), and Chemiluminescence Immunoassay (CIA).
If the RPR test is positive, but a subsequent treponemal test is negative, this discordance usually indicates a false positive RPR result. This outcome confirms that the initial RPR reactivity was not due to syphilis. Consulting with a healthcare provider is essential for interpreting these results and for any further evaluation, which may include considering a patient’s medical history and current symptoms.