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The rapid plasma reagin test (RPR test or RPR titer) is a type of rapid diagnostic test that looks for non-specific antibodies in the blood of the patient that may indicate an infection by syphilis or related non-venereal treponematoses. It is one of several nontreponemal tests for syphilis (along with the Wassermann test and the VDRL test).
This reaction is the foundation of “nontreponemal” assays such as the VDRL (Venereal Disease Research Laboratory) test and Rapid Plasma Reagin (RPR) test. Both these test are flocculation type tests that use an antigen-antibody interaction. The complexes remain suspended in solution and therefore visible due to the lipid based antigens. [3] [4]
The false positive rate is calculated as the ratio between the number of negative events wrongly categorized as positive (false positives) and the total number of actual negative events (regardless of classification). The false positive rate (or "false alarm rate") usually refers to the expectancy of the false positive ratio.
Replacement tests such as the VDRL test and the RPR test, initially based on flocculation techniques (Hinton), have been shown to produce far fewer false positive results. [ citation needed ] Indeed, the "biologic false positives" of modern tests usually indicate a serious alternate condition, often an autoimmune disease .
The log diagnostic odds ratio can also be used to study the trade-off between sensitivity and specificity [5] [6] by expressing the log diagnostic odds ratio in terms of the logit of the true positive rate (sensitivity) and false positive rate (1 − specificity), and by additionally constructing a measure, :
The false positive rate (FPR) is the proportion of all negatives that still yield positive test outcomes, i.e., the conditional probability of a positive test result given an event that was not present. The false positive rate is equal to the significance level. The specificity of the test is equal to 1 minus the false positive rate.
The rapid plasma reagin (RPR) test uses the same antigen as the VDRL, but in that test, it has been bound to several other molecules, including a carbon particle to allow visualization of the flocculation reaction without the need of a microscope. Many other medical conditions can produce false positive results, including some viruses ...
Serological assays may give a false positive result, causing the individual to appear to have seroconverted when the individual has not. False positives can occur due to the test reacting to, or detecting, an antibody that happens to be sufficiently similar in structure to the target antibody.