What Is a VDRL test?

Syphilis
Scanning Electron Micrograph of Syphilis Bacteria. CDC/SCIENCE PHOTO LIBRARY/GETTY IMAGES

VDRL is a blood test that is used to determine whether or not you have an active syphilis infection.

Although a positive VDRL test usually means that you have syphilis, that's not always the case. VDRL looks for antibodies to a non-syphilis specific protein called cardiolipin. Unfortunately, that means there can be false positive test results. False positives occur in 1 to 2 percent of the population.

They can be caused by many conditions including pregnancy, HIV infection, tuberculosis and certain other bacterial infections.

A VDRL test can be used to detect new syphilis infections. It can also be used to follow the course of syphilis treatment. How does that work? The levels of anti-cardiolipin antibodies in the blood will change depending on how active a syphilis infection is in the body. Therefore, if treatment is working, numbers can go down. Unfortunately, false positives aren't the only potential problem with the VDRL test. Over the long-term, latent syphilis infections can lead to false negative tests. 

Did You Know? VDRL stands for  "Venereal Disease Research Laboratory."

What are Other Syphilis Tests?

RPR is another non-specific test for syphilis that is used in similar ways to VDRL. Both RPR and VDRL are known as nontreponemal tests.

There are also more specific tests for syphilis.

These tests look specifically for antibodies to the organism that causes the disease - Treponema pallidum. Treponemal tests are somewhat less likely to cause a false positive diagnosis. However, they can remain positive even after an infection has been cured. A positive treponemal test just shows someone has been infected with syphilis at some point in the past.

It doesn't show whether or not they are currently infected.

Do I Need Other Tests or Just VDRL?

It is important to know that VDRL is only designed to be used as a test for syphilis. If you are concerned you may have HIV or another STD, you will need to be tested for those diseases separately. The VDRL test can not be relied on to detect any other STD.

You may also need follow-up testing after a positive VDRL test. This type of testing is done if there is a reason to believe the VDRL test may be incorrect. For example:

  • if a person's history suggests it is unlikely they have been exposed to syphilis
  • if the person has signs and symptoms more likely to be caused by another STD
  • if there are other reasons to believe a false positive is likely, such as recent immunization 

Sources:

Nayak, S., & Acharjya, B. (2012). VDRL Test and its Interpretation. Indian Journal of Dermatology, 57(1), 3–8. http://doi.org/10.4103/0019-5154.92666

"Syphilis Testing Algorithms Using Treponemal Tests for Initial Screening --- Four Laboratories, New York City, 2005--2006" MMWR Weekly August 15, 2008, / 57(32):872-5

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