cerebrospinal fluid envelops the brain and the spine, and lumbar puncture or spinal tap is the removal of a small amount of fluid using a needle inserted between the lumbar vertebrae. characteristic findings in guillain–barré syndrome are an elevated protein level, usually greater than 0.55 g/l, and fewer than 10 white blood cells per cubic millimeter of fluid ("albuminocytological dissociation"). this pattern distinguishes guillain–barré syndrome from other conditions (such as lymphoma and poliomyelitis) in which both the protein and the cell count are elevated. elevated csf protein levels are found in approximately 50% of patients in the first 3 days after onset of weakness, which increases to 80% after the first week.