Bacterial Meningitis CSF Findings
The correct answer is B: Leukocytosis with polymorphs, low glucose, high protein. This is the classic cerebrospinal fluid profile that confirms bacterial meningitis in a child presenting with respiratory distress, fever, and neck stiffness 1.
Classic CSF Profile in Bacterial Meningitis
According to the 2016 ESCMID guidelines, the hallmark CSF abnormalities in bacterial meningitis are 1:
- Pleocytosis with predominantly polymorphonuclear leukocytes (neutrophils) - typically 80-95% neutrophils
- Low glucose concentration (<40 mg/dL in ~50-60% of cases)
- Low CSF-to-blood glucose ratio (<0.4 in children >12 months; <0.6 in neonates)
- Elevated protein levels (>120 mg/dL)
The typical WBC count ranges from 1,000-5,000 cells/mm³, though it can vary broadly from 100 to 110,000 cells/mm³ 2.
Why the Other Options Are Wrong
Option A (lymphocytes, high glucose, high protein) describes a profile more consistent with viral or tuberculous meningitis, not bacterial meningitis. Bacterial meningitis characteristically shows low glucose, not high 1.
Option C (normal leukocytes, dominant lymphocytes) would suggest either no meningitis or possibly early viral meningitis, but would not confirm bacterial meningitis.
Important Clinical Caveats
Age-Related Variations
In neonates, these classic findings may be absent 1. Studies show that 6% of neonates with proven bacterial meningitis had completely normal CSF, and 10% had fewer than 3 WBC/mm³. The median CSF WBC count in neonatal meningitis can be as low as 6 cells/mm³ 1.
Early Presentation Pitfall
Approximately 10% of bacterial meningitis patients present with lymphocyte predominance (≥50% lymphocytes) rather than neutrophil predominance 2. Research shows that 57% of children with aseptic (viral) meningitis can have PMN predominance, and this persists beyond 24 hours of illness 3. However, this does not change the classic teaching that bacterial meningitis typically shows neutrophil predominance.
Prior Antibiotic Treatment
Antibiotic pretreatment may modify CSF findings, though one study in 245 children suggested the CSF WBC count is not greatly different between those who received or did not receive antibiotics before lumbar puncture 1.
Additional Diagnostic Markers
While the question asks about confirming the diagnosis, CSF lactate has emerged as a superior discriminatory test:
- Lactate >3-4.2 mmol/L has 90-96% sensitivity and 98-100% specificity for bacterial meningitis 2, 4, 5
- CSF lactate diagnostic accuracy is better than CSF WBC count according to meta-analyses 1
Gram stain has 60-90% sensitivity and 97% specificity, with positive results in 67% of pediatric cases 2, 6.
Clinical Bottom Line
In this child with the classic triad of fever, neck stiffness, and respiratory distress, CSF showing leukocytosis with polymorphonuclear predominance, low glucose, and high protein (Option B) confirms bacterial meningitis and mandates immediate empiric antibiotic therapy with adjunctive dexamethasone 1, 2.