What are syphilis tests?

Syphilis tests generally look for certain antibodies in your blood. Antibodies are proteins that your immune system makes when it finds harmful substances in your body. In this case, the harmful substance is the bacterium that causes syphilis, one of the most common sexually transmitted infections (STIs.)

Testing usually involves two steps. The first is used to screen for antibodies that your immune system makes in response to syphilis, some autoimmune diseases, and other infections. The two most common types of this test are:

• Rapid plasma reagin (RPR), which is a blood test that looks for an antibody called reagin. Your body often makes reagin in response to a syphilis infection.
• Venereal Disease Research Laboratory (VDRL) Test, which can be done on blood or spinal fluid. This test looks for a broader range of antibodies that your immune system might make in response to a syphilis infection.

The second step in syphilis testing is to confirm the findings of the first step. If the result of your screening test shows you have antibodies linked to syphilis infections, you'll need a second test to confirm whether you have syphilis.

Usually, the second test looks for antibodies that your immune system makes only to fight off syphilis. If you have these antibodies, it means you either currently have a syphilis infection or had a syphilis infection that's been treated.

In some cases, a health care provider will use a test that looks for actual syphilis bacteria, instead of antibodies. These tests are less common because they can only be done in specialized labs.

Other names: rapid plasma reagin (RPR), Venereal Disease Research Laboratory (VDRL), fluorescent treponemal antibody absorption (FTA-ABS) test, agglutination assay (TP-PA), darkfield microscopy, Treponema pallidum particle agglutination assay (TP-PA), Fluorescent treponemal antibody absorption (FTA-ABS) test, Microhemagglutination assay for antibodies to T. pallidum (MHA-TP), T. pallidum hemagglutination assay (TPHA), T. pallidum enzyme immunoassay (TP-EIA), Chemiluminescence immunoassays (CLIA)

What are they used for?

All syphilis tests are used to check your blood for signs of a syphilis infection. Like other STIs, syphilis spreads through vaginal, oral, or anal sexual contact with someone who has the infection. It can also pass during pregnancy to the fetus.

Syphilis usually develops in the following four stages.

• First stage. This usually starts 2-12 weeks after exposure and can go unnoticed. The main symptom is a small, painless sore (chancre) on your genitals or in your mouth, anus, or rectum.
• Second stage. This usually starts 1-6 months after the chancre goes away. There are more symptoms in this stage, including fever and swollen glands.
• Third (or latent) stage. If you don't receive treatment, then your infection will enter this stage, which can last for years. Though you likely won't have symptoms during this phase, that does not mean you no longer have syphilis. The infection can still spread and cause damage.
• Fourth stage. This can start years after exposure if it isn't treated. Its symptoms are far more severe, including dementia (a mental disorder that causes memory loss) and blindness.

People are more likely to pass a syphilis infection to someone else during the infection's first phase, when it's more likely they won't have any obvious symptoms. It's therefore important to find and test for the infection early. Doing so may help to prevent the spread of syphilis to others.

Syphilis is also easiest to cure in the early stages of infection. If it's not treated and develops to a late stage, it can cause permanent damage to your health. Treatment can still help, but it will not reverse the damage. In rare cases, untreated syphilis can even cause death.

Why do I need syphilis tests?

You should get tested for syphilis if you have symptoms of the infection or if your sexual partner was recently diagnosed with it. Most symptoms usually appear in the second stage. Along with fever and swollen glands, these can include:

• Rough, red rash, usually on the palms of the hands or the bottom of the feet.
• Headache or muscle aches.
• Sore throat.
• Fatigue.
• Weight loss.
• Hair loss in patches.

Your provider may also test you for syphilis if you show any of the more serious signs of the infection's fourth stage. Along with dementia and blindness, these can include:

• Deep bone pain.
• Numbness.
• Dizziness.
• Heart damage.
• Hearing loss.

Even if you don't have symptoms, you should get tested regularly if you have a high risk of getting syphilis. You're more likely to get syphilis if you have:

• Multiple sex partners.
• A partner with multiple sex partners.
• Unprotected sex (sex without using a condom).
• An HIV infection and are sexually active.
• Another sexually transmitted disease, such as gonorrhea.
• Sex with men who have sex with men (MSM).

Ask your provider how often you should get tested.

You will also need a syphilis test if you are pregnant. If you pass it on to your fetus, it could cause serious, and sometimes deadly, health problems. If you are pregnant, the Centers for Disease Control and Prevention recommends that you have a syphilis test at your first prenatal visit. If you are more likely to become infected with syphilis, you should be tested again at 28 weeks of pregnancy and at delivery.

What happens during a syphilis test?

A syphilis test is usually a blood test. During a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

At any stage, syphilis can affect your brain, spinal cord, and nerves. If your symptoms show that syphilis may be affecting your brain and nervous system, your provider may order a syphilis test of your cerebrospinal fluid (CSF).

CSF is a clear fluid found in your brain and spinal cord. To get a sample of the fluid, a provider will do a procedure called a spinal tap, also known as a lumbar puncture. A spinal tap is usually done in a hospital. During the procedure:

• You will lie on your side or sit on an exam table.
• A health care provider will clean your back and inject an anesthetic into your skin, so you won't feel pain during the procedure. Your provider may put a numbing cream on your back before this injection.
• When the area on your back is completely numb, your provider will insert a thin, hollow needle between two vertebrae in your lower spine. Vertebrae are the small backbones that make up your spine.
• Your provider will withdraw a small amount of cerebrospinal fluid for testing. This will take about five minutes.
• You'll need to stay very still while the fluid is being withdrawn.
• Your provider may ask you to lie on your back for an hour or two after the procedure. This may prevent you from getting a headache afterward.

At-home syphilis test kits are also available. These kits let you collect a sample of your blood at home which you send to a lab for testing. However, these are only screening tests. In other words, they only test for antibodies to the syphilis bacteria. So, you'll still need another test to confirm your diagnosis. Talk with your provider to find out if a self-collection test is right for you.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a syphilis blood test. For a lumbar puncture, you may be asked to empty your bladder (pee) and bowels (poop) before the test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

With a spinal tap, there is also very little risk. You may feel a little pinch or pressure when the needle is inserted. After the test, you may feel some pain or tenderness in your back or have some bleeding where the needle was inserted. You may also get a headache. The headache may last for several hours or up to a week or more, but your provider may suggest treatment to relieve the pain.

What do the results mean?

If your screening test results are negative (normal), it means you probably don't have a syphilis infection. However, it doesn't completely rule out the possibility. Antibodies can take a couple of weeks to develop. So, you may need another screening test if you think you were exposed to syphilis. Your provider can tell you whether you need another test.

If your screening test results are positive, it means you have antibodies that may be from a syphilis infection. Your provider will likely order a second test to confirm whether or not you have syphilis.

If your follow-up test confirms you have syphilis, you will probably be treated with penicillin, a type of antibiotic. Antibiotic treatment cures most early-stage syphilis infections. Later-stage syphilis is also treated with antibiotics, but this treatment can't undo any damage that the syphilis caused.

If you have questions about your test results, or about syphilis, talk to your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about syphilis tests?

If you are diagnosed with syphilis, you need to tell anyone you've had sexual contact with so that they can get tested and treated if necessary. You will likely need repeat syphilis screening tests to see how well your treatment is working. Avoid sexual contact with others until testing shows you are cured.

In certain parts of the world, there are bacteria that are closely related to the bacteria that cause syphilis. These other bacteria usually spread through non-sexual skin contact with sores on a person who has an infection. They can cause diseases called yaws, bejel, and pinta. Blood tests cannot tell the difference between syphilis and their related bacteria. But a provider can make a diagnosis by looking at skin sores and asking about your medical and travel history.