A 6-year-old unvaccinated child presents with acute bacterial meningitis. CSF analysis: turbid, WBC 4500 cells/µL (95% neutrophils), glucose 10 mg/dL (blood glucose 90 mg/dL), protein 380 mg/dL. Gram stain shows gram-negative diplococci. What is the CSF:serum glucose ratio and what does it indicate?
- A CSF glucose is normal at 10 mg/dL; viral meningitis more likely
- B CSF:serum glucose ratio 0.5; borderline; consider tuberculous meningitis
- C CSF:serum glucose ratio 0.11 (<0.6 is normal for bacterial meningitis); very low ratio is characteristic of bacterial meningitis ✓
- D Glucose ratio is irrelevant; gram stain alone confirms the diagnosis
Explanation
Normal CSF:serum glucose ratio is 0.6 or above (CSF glucose is approximately 60-70% of blood glucose). In bacterial meningitis, bacteria and activated leukocytes consume glucose rapidly, dropping the ratio below 0.4 (often much lower). Here: CSF glucose 10 mg/dL ÷ blood glucose 90 mg/dL = 0.11, profoundly reduced. Combined with neutrophilic pleocytosis >1000 cells/µL, protein >200 mg/dL, and positive gram stain, this unequivocally indicates acute bacterial meningitis. Gram-negative diplococci in a child suggests N. meningitidis (or H. influenzae, though less common post-Hib vaccination).
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.