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Investigation | Comment | |
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Blood: | | |
Full blood count | Neutrophilia suggestive of bacterial infection | |
Serum glucose | Often low; allows interpretation of CSF glucose | |
Electrolytes, urea, and creatinine | To assess for complications and fluid management | |
Coagulation studies | To assess for complications | |
Blood cultures | Positive in 40–90% depending on organism | |
Inflammatory markers | Elevation suggestive of bacterial infection; procalcitonin of more value; neither can establish nor exclude diagnosis | |
CRP, procalcitonin | |
|
CSF: | | |
Protein and glucose | | |
Microscopy, culture, and sensitivities | Gram stain: S. pneumoniae—gram +ve cocci N. menigitidis—gram −ve cocci H. influenzae—gram −ve rod | |
Latex agglutination1 | Rapid; not 100% specific or diagnostic | |
PCR2 | Rapid; good sensitivity, techniques improving | |
Lactate | Routine use not currently recommended | |
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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 | |
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Other: PCR on blood or urine | Useful if CSF not obtainable | |
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