RPR (rapid plasma reagin) is a screening test for syphilis. It looks for antibodies that are present in the blood of people who have the disease.

The test is similar to the venereal disease research laboratory (VDRL) test.

Rapid plasma reagin test; Syphilis screening test

A blood sample is needed. For information on how this is done, see: Venipuncture

No special preparation is usually needed.

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, you may feel some throbbing.

The RPR test can be used to diagnose 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.

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 persons with early- and late-stage syphilis. More testing may be needed before ruling out syphilis.

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.

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
• Malaria
• Pregnancy
• 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 patient 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)

Tramont EC. Treponema pallidum (syphilis). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 238.

Workowski KA, Berman S; Centers for Disease Control and Prevention (CDC). Sexually transmitted diseases treatment guidelines, 2010. MMWR Recomm Rep. 2010;59(RR-12):1-110.

U.S. Preventive Services Task Force. Screening for syphilis infection in pregnancy: U.S. Preventive Services Task Force reaffirmation recommendation statement. Ann Intern Med. 2009;150:705-709.

U.S. Preventive Services Task Force. Screening for syphilis infection. Topic Page. July 2004. Agency for Healthcare Research and Quality, Rockville, MD. Acccessed 7/14/2012.

Hook EW III. Syphilis. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 327