The diagnosis of certain peripheral neuropathies often requires the study of spinal fluid. The procedure used to obtain spinal fluid is called the lumbar puncture (LP). A lumbar puncture, also called a spinal tap, is a procedure in which some of the fluid surrounding the spinal cord (called the cerebrospinal fluid or CSF) is withdrawn through a needle and examined in a laboratory. You will also have blood drawn, which is needed with the CSF for comparison studies.