”Some false positive nontreponemal test results are transitory and are related to an acute event, such as an acute febrile illness (eg, endocarditis, rickettsial disease) or recent immunization. Test abnormalities attributed to these conditions typically last for six months or less.
Other etiologies for false positive results of nontreponemal testing include a variety of chronic conditions, such as autoimmune disorders (particularly systemic lupus erythematosus), intravenous drug use, chronic liver disease, and perhaps underlying HIV disease.”
It is very important that each reactive nontreponemal test be followed with specific treponemal testing to determine if the result may be a false positive test or indicative of active syphilis.
UptoDate:Diagnostic testing for syphilis