Rigidity of neck muscles with flexion
With flexed hip at 90°, extension of knee produces pain
Involuntary lifting of legs with passive flexion of the neck
Horizontal rotation of the head at frequency of 2 rotations/second
Exacerbation of pre-existing headache is positive test.
^Although a 1991 study showed high sensitivity with this test, multiple newer studies have cast doubt on its sensitivity. Although it may be clinically useful in the right subset of patients, it should not be considered to be 100% sensitive.
^Normal or lower WBC results may be found in immunocompromised, early, or partially treated (e.g. with oral antibiotics) bacterial menintigis, and those with tuberculosis<unk> 
^^Lymph predominance may be found in patients with early bacterial<unk>  or those that have been partially treated (e.g. with oral antibiotics)
^^^For unexplained elevations of protein, consider encephalitis, MS, Guillian Barre
Corrections
WBC correction (for bloody tap)
Simplified version (if peripheral WBC and RBC counts are within normal limits):
Subtract 1 WBC for every 750 RBC in CSF
Complex version (WBC and/or RBC not within normal limits):
"WBCs added" = WBC(blood) x [RBC(CSF) / RBC(blood)]
WBC counted/resulted - "WBCs added" = actual WBC
Protein correction (for bloody tap)
For each 1000 RBC decrease protein value by 1mg/dl
Simplified version (if peripheral WBC and RBC counts are within normal limits):
Subtract 1 WBC for every 750 RBC in CSF
Complex version (WBC and/or RBC not within normal limits):
"WBCs added" = WBC(blood) x [RBC(CSF) / RBC(blood)]
WBC counted/resulted - "WBCs added" = actual WBC
Subtract 1 WBC for every 750 RBC in CSF
"WBCs added" = WBC(blood) x [RBC(CSF) / RBC(blood)]
WBC counted/resulted - "WBCs added" = actual WBC
For each 1000 RBC decrease protein value by 1mg/dl
CSF cultures become sterile in 2 hrs after parenteral antibiotics in meningococcal<unk>  and 6 hrs in pneumococcal<unk> 
12 hrs after antibiotics: CSF glucose levels increase and protein levels decrease. CSF WBC and neutrophils are not affected
Meningitis
Migraine headache
Encephalitis
Tension headache
Meningoencephalitis
Cluster headache
Neoplastic meningitis
Meningitis/encephalitis