VDRL (Venereal Disease Research Laboratory) assay is a nontreponemal serologic test for syphilis. VDRL is the only nontreponemal test available with an antigen that can be diluted to the appropriate concentration for detecting reaginic antibodies in cerebrospinal fluid (CSF). VDRL can be performed on CSF to diagnose neurosyphilis in patients with a history of syphilis infection.
Cerebrospinal fluid should be analyzed for cell count, protein concentration and VDRL testing. In neurosyphilis, CSF cell count is >25 cells/uL and CSF protein is >150 mg/dL. VDRL is positive.
The VDRL utilizes cardiolipin-lecithin coated particles as antigen to detect reaginic antibodies. If antibodies are present in CSF, the particles flocculate, which can be observed microscopically.
CSF VDRL results are highly specific (>90%) but sensitivity is only 50%. Therefore, a reactive CSF VDRL is diagnostic of neurosyphilis, but a non-reactive result does not rule it out.
CSF VDRL may not become nonreactive after treatment for many years.
Specimen requirement is 0.5 mL of CSF collected in a sterile vial. Reference value is a non-reactive result.
The FTA-ABS test on CSF is less specific, but more sensitive than VDRL for neurosyphilis, but it is not recommended for diagnosing neurosyphilis.
References
Miller JN. Value and limitations of nontreponemal and treponemal tests in the laboratory diagnosis of syphilis. Clin Obstet Gynecol. 1975;18(1):191-203.
Marks M, et al. Diagnostic performance of PCR assays for the diagnosis of neurosyphilis: a systematic review. Sex Transm Infect. 2018;94(8):585-588.
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