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Rapid Plasma Reagin

Does this test have other names?

RPR test, syphilis test

What is this test?

The rapid plasma reagin (RPR) test is a blood test that looks for signs of syphilis. Syphilis is a sexually transmitted disease (STD) that first causes symptoms common to many other illnesses. Early symptoms include fever, swollen glands, muscle aches, and sore throat.

In addition, people who have early-stage syphilis may have lesions, or sores, that can pass the infection on to other people during sexual contact.

If undetected, syphilis can stay in the body for years, causing damage to internal organs. Eventually, it can cause numbness, paralysis, blindness, and even death. But it can be easily cured if treated in the early stages.

The RPR test looks for antibodies that react to syphilis in the blood. This means the test doesn't detect T. pallidum, the actual bacterium that causes syphilis. Instead, it looks for antibodies against substances given off by cells that have been harmed by the bacteria. 

Why do I need this test?

You may have this test if you have ever been sexually active and show signs of syphilis. These signs may include:

  • Small, painless sore, called a chancre, at the place where syphilis invaded your body

  • Skin rash, sometimes on the palms of your hands or the bottoms of your feet

  • Fever

  • Swollen lymph glands

  • Hair loss

  • Headaches

  • Muscle aches

  • Weight loss

  • Fatigue

Years after the initial infection, in the final stages of the disease, symptoms include numbness, paralysis, blindness, and dementia.

The RPR test is often used to monitor treatment of a syphilis infection. If you are being treated for syphilis, you need to stop having sex until your sores have healed completely. In addition, your partner(s) should be notified so they can also be tested and treated if necessary.

If you are a sexually active adult with HIV/AIDS, your health care provider will likely order the RPR test at least once a year. In addition, screenings for syphilis and other STDs are recommended every three to six months if you have had unprotected sex, multiple sex partners, or intercourse while under the influence of illicit drugs, including methamphetamine.

Your health care provider may also order the RPR test if you are in a group that is at high risk for syphilis, such as sex workers, men who have sex with men, or adult prisoners. Also, because syphilis can infect and even kill a developing baby, pregnant women should be screened to avoid passing the disease to the fetus. 

What other tests might I have along with this test?

If your RPR test is positive, you will need additional tests to confirm that you have syphilis. One of the most common tests used to confirm a syphilis diagnosis is the T. pallidum enzyme immunoassay. Other tests may include:

  • Fluorescent treponemal antibody absorption

  • Microhemagglutination test for antibodies to T. pallidum

  • T. pallidum particle agglutination assay

These tests will generally rule out a false-positive result, which means your test is positive even if you don't have syphilis. Your health care provider may also be able to detect the syphilis bacteria by taking a sample from a moist lesion and looking at it under a microscope. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

A normal result is negative or nonreactive. This means you don't have syphilis. Positive results are given as a ratio in titers, which tells your doctor the amount of antibodies in your blood.

Here are some general results:

  • If you have a history of syphilis and your RPR test is negative or nonreactive, it is likely that you no longer have syphilis.

  • A positive RPR test should be followed by another type of test to diagnose syphilis.

  • If you have been treated for syphilis in the past, an RPR test that shows a titer increase of fourfold means you likely have a new syphilis infection.   

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.  

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Your test results may be false-positive for many reasons. These include pregnancy, intravenous drug use, tuberculosis, chronic liver disease, recent immunizations, or inflammation of the heart lining or valves, a condition called endocarditis. You may also have a false-positive result if you have one of a number of infections, such as a rickettsial infection like typhus or Rocky Mountain spotted fever.

Your results may be false-negative if the test is done too soon after you are infected with syphilis. It takes 14 to 21 days after infection with the spirochetes for your body's immune response to be found by the test. Drinking alcohol within 24 hours of the test also can give a false-negative result. 

How do I get ready for this test?

You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.