A clear CSF is not always a normal CSF.

A normal initial cerebrospinal fluid (CSF) study has been traditionally used to exclude the potential diagnosis of bacterial meningitis. However, cases of pyogenic meningitis in the absence of CSF pleocytosis have been reported in which smears for gram stain or CSF culture revealed the diagnosis of meningitis. In the presence of clinical signs of meningitis, an abnormal initial CSF study indicates a diagnosis of bacterial meningitis but a normal result may not necessarily exclude it and therefore, should not delay early institution of appropriate antimicrobial therapy.