The Venereal Disease Research Laboratory (VDRL) test is a blood test used to screen for syphilis, a sexually transmitted infection caused by the bacterium Treponema pallidum. The test measures the antibodies produced by the body in response to antigens produced by cells damaged by the bacteria. A positive test result means that a person may have syphilis, but it is not a definitive diagnosis. If the test is positive, the next step is to confirm the results with a more specific syphilis test, such as the FTA-ABS test. False-positive results can occur in some conditions, including HIV/AIDS and Lyme disease.

The VDRL test is a simple, sensitive, and low-cost test used for screening of syphilis. The test does not require fasting or stopping any medications. Usually, a healthcare professional will draw blood from a vein at the crease of the elbow or the back of the hand, and the blood sample will be sent to a laboratory for testing. If a doctor suspects that the syphilis infection has spread to the brain, they may choose to test the spinal fluid in addition to the blood. A negative test result suggests that a person does not have syphilis, but the VDRL test is not always accurate, and false-negative results can occur.

In summary, the VDRL test is a blood test used to screen for syphilis by measuring the antibodies produced by the body in response to antigens produced by cells damaged by the bacteria. A positive test result means that a person may have syphilis, but it is not a definitive diagnosis. False-positive and false-negative results can occur, and a more specific syphilis test may be needed to confirm the results.