WHAT IS VENEREAL DISEASE RESEARCH LABORATORY TEST (VDRL)?
Syphilis is a complex, sexually transmitted disease characterized by a wide range of symptoms that imitate other diseases. It is caused by the organism Treponema pallidum. The Venereal Disease Research Laboratory test (VDRL) is a screening test for the presence of reagin, the antibody specific for the treponemal spirochete. In this test, the sample is heat inactivated and then mixed with an antigen (cardiolipin phospholipid derived from the beef heart in complex with lecithin and coated on particles of cholesterol) to reagin. The mixture is then examined microscopically to detect flocculation of the cholesterol particles, indicating a positive test. The VDRL test is less sensitive than the rapid plasma reagin (RPR) test for primary syphilis. The test becomes reactive during primary-stage syphilis (about 14 days after a chancre is visible) and is reactive in virtually all cases of secondary-stage syphilis. Results will revert to negative with treatment or by the tertiary stage. Many biologic false-positive results are possible; thus, specificity is low. Positive results should be confirmed with the fluorescent treponemal antibody-absorbed double-stain test.