RPR test, syphilis test

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

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

If not detected, syphilis can stay in the body for years. It can harm internal organs. Over time it can cause numbness, paralysis, blindness, and even death. But it can be easily cured if treated in the early stages. Treatment is one or more shots of penicillin G benzathine.

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

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

• Small, painless sore (chancre) at the place where syphilis invaded your body

• Skin rash. Sometimes this is on the palms of your hands or the bottoms of your feet.

• Fever

• Swollen lymph glands

• Hair loss

• Headaches

• Muscle aches

• Weight loss

• Tiredness (fatigue)

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

The RPR test is often used to check treatment of a syphilis infection. If you are being treated for syphilis, you need to stop having sex until your sores have fully healed. Your partner(s) should also be told so they can also be tested and treated if needed.

If you are a sexually active adult with HIV/AIDS, you may need the RPR test at least once a year. Screenings for syphilis and other STDs are also recommended every 3 to 6 months if you have had unprotected sex, multiple sex partners, or intercourse while under the influence of illegal drugs, including methamphetamine. It is routine to be tested for syphilis and other STDs during pregnancy. Condoms help prevent the spread of syphilis. But they don't protect against sores outside the condom area.

You may also need the RPR test if you are in a group that is at high risk for syphilis. This includes sex workers, men who have sex with men, or adult prisoners. Also because syphilis can infect and even kill a developing baby, all pregnant women should be screened to lower the chance of passing the disease to the fetus. 

RPR is not specific to just syphilis. If your RPR test is positive, you will need more 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

• Tests for other STDs

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

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

A negative or nonreactive result means you don't have syphilis. Positive results are given as a ratio in titers. This tells your healthcare provider 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 if you were not fully treated in the past.   

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.

Taking a blood sample with a needle carries risks. These include bleeding, infection, bruising, or feeling lightheaded. When the needle pricks your arm, you may feel a slight sting or pain. Afterward, the site may be sore.

Your test results may be false-positive for many reasons. These include pregnancy, IV drug use, tuberculosis, chronic liver disease, recent vaccines, or inflammation of the heart lining or valves (endocarditis). You may also have a false-positive result if you have one of a number of infections. These include rickettsial infections such as 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. 

You don't need to prepare for this test. But be sure your healthcare provider 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.