Diagnostic Testing for Syphilis Antibodies

Syphilis is a sexually transmitted infection (STI). The only way to definitively diagnose syphilis is through antibody testing.

Learn more about testing for syphilis, when to get tested, how testing works, what to expect, and what to do if you test positive.

Syphilis Tests

The only way to definitively diagnose syphilis is through testing, which can help diagnose syphilis in its earliest stages, when it is easiest to treat. If left undetected and untreated, the infection can progress to more serious stages that can cause lasting damage. This can be life-threatening.

Testing for syphilis can also help prevent infection from being spread between people.

Nontreponemal Antibody Tests

A nontreponemal antibody test is a screening test that detects antibodies related to syphilis. These tests may come in three forms:

• Venereal Disease Research Laboratory test (VDRL): This can be performed using either spinal fluid or blood.
• Rapid plasma reagin (RPR): This is done using a blood test.
• Toluidine Red Unheated Serum Test (TRUST): A serological nontreponemal test for syphilis.

If a person tests positive in a nontreponemal test, the diagnosis should be confirmed using a treponemal test. Using only one form of testing is not enough to reach an accurate diagnosis.

Nontreponemal tests can return false positives due to a number of factors, including:

• Drug use
• Autoimmune disorders
• Older age

Treponemal Antibody Tests

Treponemal antibodies related to syphilis appear earlier than nontreponemal antibodies. A treponemal test helps detect these antibodies.

These tests include:

• Immunoblots
• Fluorescent treponemal antibody absorption (FTA-ABS)
• Microhemagglutination test for antibodies to T. pallidum (MHA-TP)
• T. pallidum particle agglutination assay (TPPA)
• T. pallidum enzyme immunoassay (TP-EIA)
• Chemiluminescence immunoassay (CIA)

Treponemal antibodies can be detectable for life, even with treatment. Given this, if a person tests positive when screened using a treponemal test, a nontreponemal test must also be performed.

These test are specific for detecting syphilis antibodies.

When to Get a Syphilis Test

There are several circumstances in which getting testing for syphilis is appropriate.

You should get tested for syphilis if you:

• Have symptoms of syphilis
• Are worried you might be infected with syphilis
• Have a sexual partner who has tested positive for syphilis

It's important to get tested regularly. The importance of testing increases if the above applies and if:

• You have had sex and didn't use a condom
• You have multiple sexual partners
• You have had STIs previously
• You are a man who has sex with men
• You are pregnant
  
  

How to Get Tested

Testing for syphilis isn't always a standard part of a checkup or an exam at the gynecologist. You may have to ask directly for testing.

It is important to be upfront with your healthcare provider about your history, as this will help determine what tests you need.

Testing for syphilis as well as other STIs can take place at a number of locations including:

• A healthcare provider's office
• A health department
• A community health clinic
• Planned Parenthood
  

What to Expect

As part of a diagnosis, a physical exam usually occurs. This involves a healthcare provider examining the genitals and other areas of the body to look for lesions or rashes that could be indicative of syphilis. A healthcare provider may choose from a variety of test options.

A blood test is commonly used. This test takes only a few minutes and involves taking a sample of blood from the vein in the arm.

A swab test may also be used. This involves using a swab to take samples of fluid from any sores caused by syphilis.

In some cases, syphilis can impact the spinal cord, nerves, and brain. If symptoms suggest this is the case, a syphilis test of the cerebrospinal fluid may be used.

Cerebrospinal fluid is a clear liquid in the spinal cord and brain. To capture a sample of this fluid, a lumbar puncture is necessary. This is also referred to as a spinal tap.

During a lumbar puncture, a number of things will occur:

1. You first lie on your side on a table.
2. Your back is cleaned.
3. A local anesthetic is injected into the skin so that pain won't be felt during the procedure.
4. When the back is numb, a hollow needle is inserted between the vertebrae in the lower part of the spine.
5. A small amount of fluid is taken from the spinal cord.
6. You may be instructed to lie on your back for a couple of hours following the procedure, to prevent headaches.

Following a lumbar puncture, there may be pain or a tender feeling in the area of the back where the needle was inserted. Some people may also get a headache following a lumbar puncture that may last for a few hours or for more than a week.

Test Results

If a screening test for syphilis is negative, this suggests the person tested does not have syphilis.

However, antibodies can take weeks to develop after getting infected. Given this, it may be necessary to do a second screening test in those who believe they have been exposed to the infection.

If a screening test for syphilis is positive, this indicates that antibodies that could be from a syphilis infection are present. Another test is needed to confirm a syphilis diagnosis.

Summary

Syphilis is a sexually transmitted infection. The only way to diagnose syphilis is through testing. Testing for syphilis involves two forms of antibody tests. Both are necessary for an accurate diagnosis.

Diagnosis may involve a physical exam, blood test, swab test, and cerebrospinal fluid test. Testing is important to detect infection and begin treatment. This prevents the infection from progressing to dangerous stages that can be life threatening. Testing also assists in stopping the spread of the infection to others.

A Word From Verywell

It can feel overwhelming deciding if you should be tested for an STI like syphilis. If you suspect you have been infected with syphilis or have a sexual partner who has just tested positive, don't hesitate to reach out to your healthcare provider for support and guidance.