What are syphilis tests?
Syphilis tests are used to screen for and diagnose syphilis. Syphilis is one of the most common sexually transmitted diseases (STDs). It is a bacterial infection that spreads through vaginal, oral, or anal sexual contact with someone who has the infection. It can also pass from a pregnant person to their baby.
Syphilis usually develops in stages. Each stage has different signs and symptoms that can last for weeks, months, or even years. In the beginning, the signs and symptoms may be mild. You may not notice them. So, you could have syphilis and not know it. You could pass the infection to someone else.
Syphilis is 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.
Syphilis tests can help diagnose the infection in the early stages, when it's easiest to cure. Finding and treating the infection early can also prevent the spread of syphilis to others.
Other names: rapid plasma reagin (RPR), Venereal Disease Research Laboratory (VDRL), fluorescent treponemal antibody absorption (FTA-ABS) test, agglutination assay (TP-PA), darkfield microscopy
What are they used for?
Syphilis tests screen for and diagnose syphilis by looking for certain antibodies in your blood. Antibodies are proteins that your immune system makes when it finds harmful substances in your body.
Syphilis testing usually involves two steps. In most cases, the first step is a screening test to check for antibodies that are linked to having a syphilis infection. But other things may trigger your immune system to make these antibodies, such as autoimmune diseases, other infections, and vaccinations.
Screening tests for syphilis usually include:
- Rapid plasma reagin (RPR), which is a blood test.
- Venereal Disease Research Laboratory (VDRL) test, which can be done on blood or spinal fluid
If the result of your screening test shows you have antibodies linked to syphilis infections, you'll need a second test to confirm whether or not 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 have a syphilis infection now, or you had a syphilis infection that was treated in the past. Common tests to check for syphilis antibodies include:
- 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)
In some cases, a health care provider will use a test that looks for actual syphilis bacteria, instead of antibodies. These tests are used less often because they can only be done in specialized labs.
Why do I need a syphilis test?
You should get tested for syphilis if you have symptoms of syphilis or if your sexual partner was recently diagnosed with syphilis. Symptoms usually appear about two to three weeks after infection and include:
- Small, painless sore (chancre) on the genitals, or in the mouth, anus, or rectum
- Rough, red rash, usually on the palms of the hands or the bottom of the feet
- Headache or muscle aches
- Sore throat
- Swollen glands
- Weight loss
- Hair loss in patches
Even if you don't have symptoms, you should get tested regularly if you have a high risk for 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 you how often you should get tested.
You will also need a syphilis test if you are pregnant. If you pass it to your baby, it could cause serious, and sometimes deadly, health problems in the baby.
The Centers for Disease Control and Prevention recommends that all pregnant people have a syphilis test at their first prenatal visit. Pregnant people who are more likely to become infected with syphilis 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 lumbar puncture, also known as a spinal tap. 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.
- Once 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.
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 and bowels 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.
If you had a lumbar puncture, you may have pain or tenderness in your back where the needle was inserted. You may also get a headache after the procedure. The headache may last from a few hours to more than a week.
What do the results mean?
If your screening test results are negative (normal), it means you probably don't have a syphilis infection. But after getting infected, 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. You'll need another 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 completely 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 with 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.
You may see "self-collection" testing kits for syphilis and other sexually transmitted diseases in stores and online. These kits let you collect a sample of your blood at home which you send to a lab for testing. 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.
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.
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