Table 4: Investigations for suspected bacterial meningitis.

InvestigationComment

Blood:
 Full blood countNeutrophilia suggestive of bacterial infection
 Serum glucoseOften low; allows interpretation of CSF glucose
 Electrolytes, urea, and creatinineTo assess for complications and fluid management
 Coagulation studiesTo assess for complications
 Blood culturesPositive in 40–90% depending on organism
 Inflammatory markersElevation suggestive of bacterial infection; procalcitonin of more value; neither can establish nor exclude diagnosis
  CRP, procalcitonin

CSF:
 Protein and glucose
 Microscopy, culture, and sensitivitiesGram stain:
 S. pneumoniae—gram +ve cocci
 N. menigitidis—gram −ve cocci
 H. influenzae—gram −ve rod
 Latex agglutination1Rapid; not 100% specific or diagnostic
 PCR2Rapid; good sensitivity, techniques improving
 LactateRoutine use not currently recommended

Imaging:
 Computed tomography of the head
Indicated for focal neurology, signs of increased intracranial pressure (ICP), deteriorating neurological function, previous neurosurgical procedures, or immunocompromised
May show evidence of hydrocephalus, abscess, subdural empyema, or infarction
Normal scan does not entirely exclude risk of raised ICP

Other:
 PCR on blood or urine
Useful if CSF not obtainable

1Latex agglutination depends on laboratory availability; including N. meningitidis, S. pneumoniae, H. influenzae type B, Escherichia coli and group B streptococci.
2PCR depends on laboratory availability; including N. meningitidis, S. pneumoniae, H. influenzae type b, L. monocytogenes, HSV, CMV, Enterovirus and Mycobacterium tuberculosis.