What is the role of CSF analysis in the treatment of Haemophilus influenzae type b (Hib) meningitis?

Updated: Jul 09, 2018
  • Author: Prateek Lohia, MD, MHA; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Although CSF assays may be less sensitive or specific than positive cultures and Gram stains (unless the CSF findings are very abnormal), the results of CSF analysis are critical for the initial management of Hib meningitis. Evidence suggests that in cases where the clinical picture is consistent, any of the following CSF results predict bacterial meningitis with 99% certainty:

  • CSF glucose less than 34 mg/dL

  • CSF-to-serum-glucose ratio less than 0.23

  • CSF leukocyte count greater than 2000/µL

  • CSF neutrophil counts greater than 1180/µL

Moreover, in cases where individuals have been treated with antibiotics within the week before the lumbar puncture, the less-irrefutable approach of diagnosing meningitis by CSF cell counts and chemistries must nonetheless be relied upon for decisions concerning initiation and continuation of therapy. Two careful prospective studies indicate that as many as one third of children with Hib meningitis have received recent antibiotic treatment, usually for suspected otitis media.

Previous treatment with oral antibiotics may significantly reduce the yield of CSF culture and Gram stain; indeed, these may be rendered negative within 24 hours of such treatment. CSF protein concentration and neutrophil percentage are also decreased. On the other hand, previous treatment has not been shown to significantly decrease the yield of blood culture, total CSF WBC count, CSF glucose concentration, or CSF-to-serum-glucose ratio.

The reduced significance of some of these indicators of bacterial meningitis was thought to be due to the fact that oral antibiotics, while not preventing the development of meningitis, had attenuated the severity of illness. This concept is supported by the finding that among children whose Hib meningitis was preceded by otitis media or upper respiratory illness, the interval between the preceding illness and the development of meningitis was several days longer in children who received antibiotic treatment than in untreated children.

Studies of the effects of IV antibiotic administration on CSF characteristics of children with meningitis have shown that as many as several days of IV treatment with appropriate antibiotics does not significantly alter CSF protein, glucose, or WBC concentrations, although the yield of Gram stain and culture is lost.

No results of CSF cell counts or chemistries can be used to irrefutably rule out a meningitis diagnosis in a patient who has clinical indications of possible meningitis. This is particularly true because of the possibility of viral meningitis in such cases.

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