No single exam finding can rule in or rule out meningitis.
Acute bacterial meningitis develops rapidly and patients will generally exhibit at least two of:
Mental status change
Routine: culture, gram stain, protein, glucose, cell count and differential, viral PCR (HSV, VZV, enterovirus)
Consider: CSF VDRL and serum syphilis serology, fungal culture/cryptococcal antigen/serum cryptococcal antigen, acid fast bacilli, West Nile PCR/serology