The venereal disease research laboratory test (VDRL) is a blood test that can identify syphilis infections. Syphilis is one of the most common sexually transmitted infections (STIs).
The Centers for Disease Control and Prevention (CDC) reported 115,045 new syphilis diagnoses during 2018.
Untreated syphilis can damage vital organs, including the brain, spinal cord, and heart.
With the help of screening and testing procedures, doctors can diagnose syphilis and other STIs in the early stages.
This article will look at the VDRL test, which is one type of syphilis screening test.
The VDRL test is 1 of 3 nontreponemal tests for detecting syphilis. Nontreponemal tests are not specific to syphilis and can yield false-positive results.
Doctors cannot diagnose syphilis infections based on positive VDRL results alone. They need to confirm the infection with a treponemal test, which is specific to syphilis.
A doctor may perform a VDRL test on either the blood or the cerebral spinal fluid (CSF).
A VDRL test on the CSF typically occurs if a doctor suspects that the syphilis is at a more advanced stage when it can affect the brain and central nervous system. This is called neurosyphilis.
For this test, a doctor will collect CSF through a procedure called a lumbar puncture, also known as a spinal tap.
How does it work?
The Treponema pallidum (T. pallidum) bacterium causes syphilis infections.
When T. pallidum enters the body, the immune system produces antibodies, which are proteins that destroy the invading bacteria.
The VDRL test does not react to the T. pallidum bacterium. Instead, the test measures the number of antibodies present in the blood or CSF.
Healthcare providers collect a sample of blood or spinal fluid and send it off to a laboratory where a technician will test it for antibodies.
A VDLR test on blood involves adding a colorless alcoholic solution consisting of beef cardiolipin, lecithin, and cholesterol to the blood sample.
A CSF test involves adding a mixture of lipids, called reagin. If clumping occurs, this indicates a positive reaction and, therefore, the presence of syphilis.
In most situations, healthcare providers perform VDRL tests by taking blood samples. However, they can perform the test using a sample of CSF.
A blood draw involves a healthcare provider inserting a hollow needle into a vein in the elbow or on the back of the hand.
The blood flows into an airtight collection tube attached to the other end of the needle.
A healthcare provider may tie a rubber band, or tourniquet, above the injection site before inserting the needle to make the veins easier to locate.
Healthcare providers collect samples of CSF through a procedure known as a lumbar puncture or spinal tap.
During the procedure, a person will lie on their side and pull their knees towards their chest.
The healthcare provider will disinfect and numb the injection site with a local anesthetic.
Then they will insert a spinal needle into the lower spine, which they use to extract a small quantity of CSF.
The laboratory will send the results to the doctor who ordered the test.
The doctor will explain a person’s test results either at a follow-up appointment or over the phone.
The test can take 3–5 days.
Negative test results typically mean that the blood does not contain any antibodies to syphilis.
A negative VDRL blood test result suggests there is no evidence of an infection.
Typically, people who get a negative result do not require additional testing.
However, people who have a high risk of syphilis may want to consider getting routine screening tests about every 3 months.
According to the New York City Department of Health and Mental Hygiene Bureau of Sexually Transmitted Infections, a negative CSF result does not rule out a diagnosis of neurosyphilis.
A positive result means that the VDRL test detected the presence of the syphilis antibodies.
If the result is positive, a doctor will perform another test, such as the fluorescent treponemal absorption assay. This test will be able to confirm whether the infection is syphilis.
Typically, a doctor will recommend a VDRL test on CSF when they suspect a person has late stages of syphilis.
If a person receives a positive result, a doctor will typically perform a treponemal test, which detects the antibodies to the T Pallidum proteins. If this is positive, it indicates that syphilis has infected the central nervous system.
Sometimes, however, doctors test for syphilis in reverse. They will begin by testing a person with a syphilis-specific treponemal test. If this proves positive, they will follow it up with a nontreponemal test, such as a VDRL
The VDRL test offers a safe and convenient way to screen for syphilis infections. The test itself does not carry any significant risks.
However, there may be some slight complications associated with the process of drawing blood and lumbar punctures.
Blood draws may cause:
- tenderness or pain near the injection site
- bruising or bleeding immediately after the procedure
Although rare, a lumbar puncture can cause the following complications:
- a mild to severe headache
- numbness or tingling in the lower back or legs
- lower back or leg pain
- infections at the injection site
The United States Preventative Services Task Force (USPSTS) recommend screening for syphilis infections in the following populations:
- men who have sex with men
- people living with HIV
- pregnant women
A doctor may use a VDRL test to screen for syphilis if someone:
- has symptoms of syphilis
- has recently been treated for syphilis
- believes they may have had exposure to T. pallidum
- is currently receiving treatment for another STI
- engages in sexual activity without the use of barrier contraceptives
A person should get tested for syphilis if they experience the following symptoms.
- The appearance of a chancre: This is a painless, round, firm sore. The chancre will heal after 3–6 weeks, even if a person does not receive treatment.
- The appearance of rashes or sores: The rash may be red and rough, and sores may appear on areas of the body.
Other symptoms may include swollen lymph glands, fever, hair loss, weight loss, and headaches.
Symptoms of syphilis vary according to the stage of the disease.
A chancre appears during the primary stage of syphilis. It will appear where the infection entered a person’s body.
If a person does not receive treatment, syphilis will develop into the secondary stage.
This is when skin rashes and lesions appear. They may occur in the vagina, the anus, or the mouth.
The rashes are not typically itchy.
A person may also develop a fever, muscle aches, swollen lymph glands, sore throat, and hair loss.
No symptoms of syphilis appear in this stage.
This stage can be fatal and typically occurs between 10–30 years after the initial infection.
It can affect the brain, eyes, heart, blood vessels, joints, and bones.
The symptoms may vary depending on which organ the syphilis is affecting.
Neurosyphilis and Ocular Syphilis
This can occur at any stage of the infection. Ocular syphilis affects the eyes, and neurosyphilis affects the brain and nervous system.
Symptoms include headaches, paralysis, dementia, difficulty coordinating muscles, and a change in behavior.
Doctors and other healthcare providers use the VDRL test to screen for syphilis. Syphilis is an STI caused by the T. pallidum bacterium.
The body’s immune system produces antibodies that kill bacteria and other potentially harmful microbes.
The VDRL test measures the number of antibodies present in a person’s blood or spinal fluid.
In order to perform the test, a healthcare provider must collect blood or a sample of spinal fluid.
These procedures can cause minor side effects, such as headaches, bruising, and soreness near the injection site.
People who have negative results mostly likely do not have syphilis. However, a doctor may recommend repeating the test at a later date if someone had a recent exposure or has a high risk for syphilis.
Detecting syphilis in the early stages can lead to better, more effective treatment outcomes.
Early treatment reduces the risk of long-term complications and helps prevent further transmission.