RPR (rapid plasma reagin) is a screening test for syphilis. It looks for antibodies that are present in the blood of people who may have the disease.
Rapid plasma reagin test; Syphilis screening test
How the Test is Performed
How to Prepare for the Test
No special preparation is usually needed.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Why the Test is Performed
The RPR test can be used to screen for syphilis. It is used to screen people who have symptoms of sexually transmitted infections and is routinely used to screen pregnant women for the disease.
Several states also require that couples be screened for syphilis before getting a marriage license.
The test is also used to see how treatment for syphilis is working. After treatment with antibiotics, the levels of syphilis antibodies should fall. These levels can be monitored with another RPR test. Unchanged or rising levels can mean a persistent infection.
The test is similar to the venereal disease research laboratory (VDRL) test.
A negative test result is considered normal. However, the body does not always produce antibodies specifically in response to the syphilis bacteria, so the test is not always accurate. False-negatives may occur in people with early- and late-stage syphilis. More testing may be needed before ruling out syphilis.
What Abnormal Results Mean
A positive test result may mean that you have syphilis. If the screening test is positive, the next step is to confirm the diagnosis with a more specific test for syphilis, such as FTA-ABS. The FTA-ABS test will help distinguish between syphilis and other infections or conditions.
How well the RPR test can detect syphilis depends on the stage of the infection. The test is most sensitive (almost 100%) during the middle stages of syphilis. It is less sensitive during the earlier and later stages of the infection.
Some conditions may cause a false-positive test, including:
- IV drug use
- Lyme disease
- Certain types of pneumonia
- Systemic lupus erythematosus and some other autoimmune disorders
- Tuberculosis (TB)
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
LaSala PR, Smith MB. Spirochete infections. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 59.
Radolf JD, Tramont EC, Salazar JC. Syphilis (Treponema pallidum). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 239.
Reviewed By: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.