The RPR and VDRL tests are nontreponemal tests, meaning that they do not identify the bacterium or the antibodies unique to syphilis. These tests indicate the presence of reagin antibodies. Reagin is a nonspecific type of antibody that can occur during many types of infection other than syphilis. Since these tests are only initial screening tests, the more sophisticated treponemal tests must be used to confirm the diagnosis.
As with all venous blood samples taken from the inner crease of the arm, special precautions should be taken for compromised patients. Health care providers should avoid drawing a blood sample from the arm that also has an intravenous line, is edematous, or has scar tissue, an existing hematoma, or damaged veins. As with all blood samples or body fluid collections, health care providers should use standard precautions to protect themselves and others from exposure to the potentially infectious samples or equipment used to obtain the samples.
Biological false-positive results
There are many conditions that can cause a false-positive test result when a patient is tested for syphilis with RPR or VDRL tests. Conditions that can produce a reactive test result include: