What is the role of CSF white blood cell count in the workup 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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Answer

CSF should be examined promptly for WBCs because these cells generally begin to disintegrate within about 90 minutes of the lumbar puncture. WBC levels greater than 10/µL are usually considered abnormal, as is the presence of even 1 polymorphonuclear (PMN) leukocyte.

WBC differential counts from cytocentrifuged CSF may falsely elevate the PMN leukocyte count. The occurrence of a preceding convulsive seizure may elevate the WBC count, particularly the PMN leukocyte count. When modest CSF pleocytosis is due to seizure and not meningitis, opening pressure is usually normal, CSF is clear, fewer than 80 WBC/µL are found, and CSF glucose is normal.

The typical finding in Hib meningitis is PMN leukocyte–predominant pleocytosis, as is the case in most other forms of bacterial meningitis. CSF WBC counts in Hib meningitis are greater than 100/µL in more than 90% of cases and greater than 1000 in 65-70% of cases. The mean CSF WBC counts for Hib meningitis approach 1100/µL.

Note, however, that although lymphocytes typically predominate in the fully developed CSF pleocytosis of viral meningitis, PMN leukocytes may predominate in as many as 20-75% of lumbar puncture samples obtained in the early phases of viral encephalitis, and they may be found in 5-8% of viral encephalitides even after fully developed pleocytosis has been achieved. On the other hand, approximately 10-30% of bacterial meningitis cases have early lymphocytic predominance, especially in cases where the CSF WBC count is fewer than 1000/µL.

In at least half of all patients who receive appropriate antibiotic therapy for bacterial meningitis, the CSF WBC count remains elevated for at least 1 week after initiation of therapy. In some cases, the elevation persists for several weeks. However, falling CSF WBC counts on repeat lumbar punctures should be considered a reassuring indication of response to appropriate treatment.

Relatively low CSF WBC counts in a very ill child with Hib meningitis may indicate a poor prognosis, especially if large numbers of nonengulfed Hib organisms are observed on the CSF Gram stain.


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