What Is a VDRL Test?
The venereal disease research laboratory (VDRL) test is designed
to assess whether or not you have syphilis, a sexually transmitted infection
(STI). Syphilis is caused by the bacteria Treponema
pallidum. The bacteria infects by penetrating into the lining of the mouth
or genital area.
The VDRL test doesn’t look for the bacteria that causes 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 whether or not you currently have
Why Doctors Perform a VDRL Test
Your doctor will most likely order a VDRL test if there is 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. The
Disease Control and Prevention (CDC) also recommends follow-up testing if
you have been treated for syphilis to be sure that the treatment worked and the
infection has been cured.
The VDRL Test
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 to
a laboratory and tested for the antibodies produced as a result of syphilis.
The VDRL test generally 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
instead of your blood.
Understanding the Results of Your VDRL Test
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.
Potential for False Positives and Negatives
The VDRL test isn’t always accurate. For example, you may have
false-negative results if you have had syphilis for less than three months, as
your body might take this long 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.
Risks of Taking the VDRL 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.