The CSF VDRL test is a laboratory test used to detect the presence of antibodies against Treponema pallidum, the bacterium responsible for syphilis, in the cerebrospinal fluid (CSF). The test is performed by collecting a sample of CSF through a lumbar puncture (spinal tap), and then analyzing it for signs of infection. The CSF VDRL test is primarily used to diagnose neurosyphilis, a condition where syphilis affects the nervous system, which can occur in untreated or late-stage syphilis. It is typically administered when a patient shows symptoms of neurosyphilis, such as cognitive changes, meningitis, or abnormal behavior, or in cases where there is a suspicion of syphilis affecting the central nervous system. The test is also used to monitor treatment efficacy in patients diagnosed with neurosyphilis.