Which test would likely have been requested earlier for a patient showing signs of syphilis?

The Rapid Plasma Reagin (RPR) test is a non-treponemal test used for the screening of syphilis. It detects certain antibodies that are produced in response to the presence of the Treponema pallidum bacteria, the causative agent of syphilis. Given that the question pertains specifically to a patient showing signs of syphilis, RPR is the most relevant test because it directly addresses the diagnosis of syphilis and serves as an initial screening tool.

When considering the other tests mentioned, while an HIV test might be relevant due to the association between syphilis and HIV, it is not specific to diagnosing syphilis itself. Lyme serology is used to determine Lyme disease, which is unrelated to syphilis, and chlamydia screening targets a different sexually transmitted infection. Thus, RPR would be the most appropriate and immediately relevant test to request for a patient exhibiting signs of syphilis, making it the effective choice in this scenario.