339 - Assessing Utilization of the Venereal Disease Research Laboratory Test in Cerebrospinal Fluid for the Diagnosis of Neurosyphilis: A Cohort Study

Background: The Venereal Disease Research Laboratory (VDRL) test performed in cerebrospinal fluid (CSF) is considered highly specific for the diagnosis of neurosyphilis, but algorithms to diagnose neurosyphilis require positive syphilis serologic testing prior to obtaining CSF-VDRL. Inappropriate use of diagnostic tests depletes healthcare resources, and contributes to rising healthcare expenditures. CSF-VDRL has historically been improperly utilized; however there is no recent evaluation of its use in clinical practice. We aimed to quantify rates of appropriate CSF-VDRL testing, determine the CSF-VDRL false-positivity rate and describe causes of false-positive CSF-VDRL reactivity.

Methods: In this retrospective cohort study of three Mayo Clinic sites (Rochester, MN, Jacksonville, FL, and Scottsdale, AZ), we measured the rate of appropriate CSF-VDRL test utilization in patients with negative testing from January 1, 2011 to December 31, 2017. We then identified all patients with positive CSF-VDRL testing from January 1, 1994 to February 28, 2018, characterized true- and false-positive rates and described causes of CSF-VDRL false-positivity.

Results: Among 8,553 persons with negative CSF-VDRL results, testing was unnecessarily ordered in 8,399 (98.2%). The word “syphilis” or “neurosyphilis” appeared in the notes of only 1,184 (13.8%) individuals with a negative CSF-VDRL result. From January 1994 through February 2018, 33,933 CSF-VDRL tests were performed on 32,626 individual patients. Among 60 positive CSF-VDRL results, 41 (68.3%) were true-positives, 2 (3.3%) were indeterminate, and 17 (28.3%) were false-positives. Every patient with true-positive CSF-VDRL had positive serologic syphilis testing prior to CSF testing. All patients with false-positive CSF-VDRL results were inappropriately tested. Neoplastic meningitis was a common cause of false-positive CSF-VDRL results.

Conclusion: This is the first study in decades to review CSF-VDRL utilization for the diagnosis of neurosyphilis. Inappropriate use of CSF-VDRL testing for diagnosis of neurosyphilis remains problematic in clinical practice. Following recommended testing algorithms would prevent unnecessary testing, preserve resources, and minimize false-positive results.