Lumbar puncture is performed to measure the opening pressure, as well as to obtain cerebrospinal fluid (CSF) to exclude alternative diagnoses. If the opening pressure is increased, CSF may be removed for transient relief (see below). The CSF is examined for abnormal cells, infections, antibody levels, the glucose level, and protein levels. By definition, all of these are within their normal limits in IIH. Occasionally, the CSF pressure measurement may be normal despite very suggestive symptoms. This may be attributable to the fact that CSF pressure may fluctuate over the course of the normal day. If the suspicion of problems remains high, it may be necessary to perform more long-term monitoring of the ICP by a pressure catheter.