VDRL (Venereal Disease Research Laboratory) and RPR (Rapid Plasma Reagin) tests are non-treponemal screening tests used for the diagnosis of syphilis. These tests detect non-specific antibodies (reacting to lipids) produced by the body in response to infection with Treponema pallidum, the causative agent of syphilis. Both methods are used as initial screening tests and, due to their simplicity and low cost, are commonly applied in screening high-risk populations or pregnant women. Positive results from these tests must be confirmed with specific treponemal tests (such as FTA-ABS or TP-PA), because false positives can occur in other conditions like autoimmune diseases, pregnancy, or viral infections. The antibody titer level in these tests is also useful for monitoring the response to syphilis treatment. The RPR test is considered an improved version of the VDRL test, using carbon particles to increase sensitivity and allowing the test to be performed on plasma (not only cerebrospinal fluid).