Laboratory Tests 41718

• CSF examination via lumbar puncture (LP, spinal tap); contraindicated in patients with cardiorespiratory compromise, increased intracranial pressure and papille-dema, focal neurologic signs, seizures, bleeding disorders, abnormal level of consciousness, and possible brain herniation (a CT scan should be performed before LP if there is a question of a CNS mass to avoid potential for brain herniation) (see Table 70-2 for specific CSF findings)

• Elevated opening pressure (may be decreased in neonates, infants, and children)

• Decreased glucose

• Elevated protein

• Elevated WBC (differential provides clues to offending pathogen)

• Gram stain (adequate for diagnosis in 60-90% of patients with bacterial meningitis)

• Culture and sensitivity (positive in 70-85% without prior antibiotic therapy, positive in less than 20% who have had prior therapy)

• If CSF Gram stain and/or culture is negative, rapid diagnostic tests (such as latex agglutination) may be useful; these tests are positive even if bacteria are dead

• Polymerase chain reaction (PCR; DNA amplification of the most common bacterial meningitis pathogens) may be useful to help exclude bacterial meningitis

• Elevated CSF lactate and C-reactive protein

• Blood cultures (at least two cultures, one "set"; positive in 66%)

• Scraping of skin lesions (such as rash) for direct microscopic examination and culture

• Other cultures should be obtained as clinically indicated (such as sputum)

• WBC with differential

• Fungal meningitis: CSF culture, CSF and serum cryptococcal antigen titers, microscopic examination of CSF specimens

• Tuberculous meningitis: CSF culture, PCR evaluation (preferred), and acid-fast stain

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