The Venereal Disease Research Laboratory test (VDRL) is a screening blood test for syphilis and related non-venereal treponematoses that were developed by the eponymous lab. It measures substances (proteins), called antibodies, that your body may produce if you have come in contact with the bacteria that cause syphilis. The VDRL test is used to screen for syphilis (it has high sensitivity), whereas other, more specific tests are used to diagnose the disease. Prozone phenomenon and biological false positive (BFP) reaction are two shortcomings of this test.
A positive test result means you may have syphilis. If the test is positive, the next step is to confirm the results with an FTA-ABS test, which is a more specific syphilis test. The VDRL test’s ability to detect syphilis depends on the stage of the disease.
How the Test is Performed
The test is most often done using a blood sample. It can also be done using a sample of spinal fluid. This article discusses the blood test.
A blood sample is needed.
How the Test will Feel
When the needle is inserted to draw blood, some people may feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
This test is used to screen for syphilis . The bacteria that cause syphilis is called Treponema pallidum.
Your health care provider may order this test if you have signs and symptoms of a sexually transmitted illness (STI).
Syphilis screening is a routine part of prenatal care during pregnancy. Several states also require screening for syphilis prior to obtaining a marriage license.
This test is similar to the newer rapid plasma reagin ( RPR ) test.
Normal Results
A negative test is normal. It means that no antibodies to syphilis have been seen in your blood sample.
The screening test is most likely to be positive in the secondary and latent stages of syphilis. This test may give a false-negative result during early- and late-stage syphilis. This test must be confirmed with another blood test to make the diagnosis of syphilis.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
A positive test result may mean you have syphilis. If the test is positive, the next step is to confirm the results with an FTA-ABS test, which is a more specific syphilis test.
The VDRL test’s ability to detect syphilis depends on the stage of the disease. The test’s sensitivity to detect syphilis nears 100% during the middle stages; it is less sensitive during the earlier and later stages.
Some conditions may cause a false-positive test, including:
- HIV
- Lyme disease
- Certain types of pneumonia
- Malaria
- Systemic lupus erythematosus
The body does not always produce antibodies specifically in response to the syphilis bacteria, so this test is not always accurate.
Risks
Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Potential for false positives and negatives
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:
- HIV
- Lyme disease
- malaria
- pneumonia (certain types only)
- systemic lupus erythematosus
- IV drug use
- tuberculosis
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.
References
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