The cerebrospinal fluid (CSF) glucose test measures the amount of glucose, or sugar, present in the fluid. CSF is a clear liquid that pads and environs the brain and spinal cord, which constitute your central nervous system (CNS). This fluid is instrumental is carrying nutrients to and waste away from the brain and spinal cord. A Cerebrospinal fluid test is used to diagnose many diseases affecting the brain and spinal cord. These diseases are categorized into: Infectious diseases such as meningitis and encephalitis Hemorrhaging within the brain or skull Autoimmune disorders, such as Guillain-Barré syndrome, sarcoidosis or multiple sclerosis Tumors located within the central nervous system or that spread to the central nervous system Testing a CSF sample is the best way to diagnose these conditions because CSF is in direct contact with the brain and spine.