RPR (rapid plasma reagin) is a screening test for syphilis. Syphilis is an infectious disease. The bacteria that causes it spreads through broken skin or mucous membranes. It is most often spread by sexual contact. If you have sores in the genital area or on your hands you should have this lab performed. When a person has syphilis their are antibodies that are produced in response to it. It looks for antibodies that are present in the blood of people who have the disease.