The venereal disease research laboratory (VDRL) test is designed to assess whether you have syphilis, a sexually transmitted infection (STI). Syphilis is caused by the bacterium Treponema pallidum. The bacterium infects by penetrating into the lining of the mouth or genital area.
The VDRL test doesn’t look for the bacteria that cause syphilis. Instead, it checks for the antibodies your body makes in response to antigens produced by cells damaged by the bacteria. Antibodies are a type of protein produced by your immune system to fight off invaders like bacteria or toxins. Testing for these antibodies can let your doctors know whether you have syphilis.
You don’t need to have the symptoms of syphilis for this test to be accurate. Because it checks for antibodies produced as a result of a syphilis infection, the VDRL test can be used regardless of whether you currently have any symptoms.
Your doctor will most likely order a VDRL test if there’s a chance you have syphilis. Early symptoms that may prompt your doctor to order this test include:
- one small, painless sore
- swelling in lymph nodes near the sore
- a skin rash that doesn’t itch
In other cases, your doctor may screen for syphilis even if you don’t have any symptoms or reasons to think you have the disease. For example, your doctor will screen for syphilis as a routine part of your care if you’re pregnant. This is a standard procedure, and it doesn’t mean your doctor thinks you have syphilis.
Your doctor may also test you for syphilis if you’re being treated for another STI such as gonorrhea, if you’re infected with HIV, or if you’ve engaged in high-risk sexual activity. If you’ve already been treated for syphilis, the recommend follow-up testing to be sure that the treatment worked and the infection has been cured.
Usually, all you need to do for the VDRL test is allow a healthcare professional to draw your blood. Blood is generally drawn from a vein at the crease of the elbow or the back of the hand. This blood sample will then be sent to a laboratory and tested for the antibodies produced as a result of syphilis.
The VDRL test doesn’t require you to fast or stop taking any medications. If your doctor wants you to make an exception, they’ll let you know before your test. If your doctor suspects that the syphilis infection has spread to your brain, your doctor may choose to test your spinal fluid in addition to your blood.
If your test comes back negative for syphilis antibodies, the result suggests that you don’t have syphilis.
If your test comes back positive for syphilis antibodies, you probably (but not definitely) have syphilis. If this occurs, your doctor will order a more specific test to confirm the results. A treponemal test is often used to confirm the positive test. Treponemal tests check whether your immune system has produced specific antibodies in direct response to the syphilis-causing Treponema pallidum.
The VDRL test isn’t always accurate. For example, you may have false-negative results if you’ve had syphilis for less than three months, as it could take this long for your body to make antibodies. The test is also unreliable in late-stage syphilis.
On the other hand, the following can cause false-positive results:
- Lyme disease
- pneumonia (certain types only)
- systemic lupus erythematosus
- IV drug use
In some cases, your body may not produce antibodies even if you have been infected with syphilis. This means the VDRL test will be inaccurate.
The antibodies produced as a result of a syphilis infection can stay in your body even after your syphilis has been treated. This means you might always have positive results on this test.
The risks of a blood draw are fairly minor. You might have slight issues like mild pain during the blood draw or minor bruising or bleeding afterward. Developing a serious problem from a blood draw, such as inflammation of the vein or an infection, is rare.
Syphilis is treatable, but it’s important to consult your doctor as soon as you think you might have been exposed. If it’s left untreated, it can spread through your body and cause complications in your organs. The VDRL test isn’t perfect, but it’s a trusted test that can be a first step in helping to determine if you’ve been infected. The main thing to remember is to practice safe sex, and if you think there’s a chance that you’ve had contact with syphilis, see your doctor right away.