Venereal Disease Research Laboratory test

A test for syphilis

The Venereal Disease Research Laboratory test (VDRL test) is a blood test for syphilis, a sexually transmitted infection caused by the bacterium Treponema pallidum. The test detects non-specific antibodies that the body produces in response to the infection.

Principle

The VDRL test is a type of flocculation test that detects the presence of reagin antibodies in the blood. These antibodies are not specific to Treponema pallidum but are produced in response to cellular damage caused by the infection. The test involves mixing the patient's serum with a cardiolipin-lecithin-cholesterol antigen. If reagin antibodies are present, they will bind to the antigen and form visible clumps, indicating a positive result.

Procedure

The VDRL test is performed by collecting a blood sample from the patient. The serum is separated from the blood cells and mixed with the antigen on a slide. The slide is then observed under a microscope for the presence of clumping, which indicates a positive reaction.

A VDRL test slide showing a positive reaction

Interpretation of Results

A positive VDRL test indicates the presence of reagin antibodies, which may suggest a syphilis infection. However, because the test is non-specific, it can also yield false-positive results in conditions such as lupus, malaria, and certain viral infections. Therefore, a positive VDRL test is usually confirmed with a more specific test, such as the Fluorescent Treponemal Antibody Absorption Test (FTA-ABS).

Limitations

The VDRL test is less sensitive in the early stages of syphilis and in late latent syphilis. It is also subject to false-positive results due to other medical conditions. Therefore, it is often used as a screening test, with positive results confirmed by more specific tests.

Clinical Use

The VDRL test is commonly used for screening blood donors and pregnant women for syphilis. It is also used to monitor the effectiveness of treatment in patients diagnosed with syphilis, as the antibody levels typically decrease with successful treatment.

A VDRL test slide showing a negative reaction

Related pages

• Syphilis
• Treponema pallidum
• Fluorescent Treponemal Antibody Absorption Test
• Sexually transmitted infection