Cerebrospinal fluid is a clear fluid surrounding the brain and the spinal cord. It is collected via a lumbar puncture under sterile conditions. CSF is analyzed to confirm certain diseases. Common tests performed on CSF include protein and glucose levels, cell counts and differential count, microscopic examination, stains, and cultures. CSF may also be tested for glutamine, lactate dehydrogenase, lactic acid, tumor markers and C-reactive proteins.