What is the role of lab testing in the diagnosis of pneumococcal meningitis?

Updated: Jun 08, 2020
  • Author: Eduardo Sanchez, MD; Chief Editor: John L Brusch, MD, FACP  more...
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CSF findings are typical of those found in bacterial meningitis and usually include the following:

  • Elevated opening pressure (>20 cm H 2O)
  • Elevated WBC count (1000-5000 cells/μL) with neutrophilic predominance (>80%)
  • Elevated protein level (>100 mg/dL)
  • Decreased glucose level (< 40 mg/dL; < 60% of simultaneous blood glucose)
  • Highly elevated lactic acid levels (>6 mmol/L)

Most patients with pneumococcal meningitis who do not receive antibiotics in the 4-6 hours prior to lumbar puncture will have positive results on Gram stain and/or culture.

Rapid antigen tests (eg, latex agglutination or enzyme immunosorbent assays) can be performed on CSF (as well as sputum and urine) but rarely provide information beyond what is obtained with Gram stain and culture unless antibiotics were administered to the patient prior to performing the lumbar puncture.

A multiplex PCR assay specific for meningitis/encephalitis that can detect 14 pathogens in the CSF, including S pneumoniae, has been shown to be highly specific, approaching the specificity of the reference standard method used for diagnosing meningitis/encephalitis. However, in a recent study the highest proportion of false-positive results was observed for S pneumoniae. [67]

Blood culture results are positive in up to 90% of patients.

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