CSF WBC Count Calculation for 14-Year-Old with Suspected Meningitis
The WBC count in the CSF is 1,000 cells/μL based on the information provided in the case.
Calculation Method
To determine the CSF WBC count from the given information:
- The sample showed 100 cells in 9 large squares using WBC Unopettes with 1:20 dilution
- Using the standard calculation formula for hemocytometer counting:
- WBC count (cells/μL) = (Number of cells counted × Dilution factor) ÷ (Area counted × Chamber depth)
- WBC count = (100 × 20) ÷ (9 × 0.2) = 2000 ÷ 1.8 = 1,000 cells/μL
Clinical Significance
This WBC count of 1,000 cells/μL is clinically significant and concerning in this patient with:
- Fever
- Vomiting
- Lethargy
- Neck stiffness
- Slightly cloudy CSF appearance
Interpretation in Context
- A CSF WBC count of 1,000 cells/μL strongly suggests meningitis in this adolescent patient 1
- The clinical presentation with fever, neck stiffness, and lethargy, combined with this CSF finding, is highly concerning for bacterial meningitis
- The slightly cloudy appearance of the CSF further supports this diagnosis
Differential Considerations
- Bacterial meningitis: Most concerning given the clinical presentation and CSF findings
- Viral meningitis: Typically has lower WBC counts but can reach this level
- Partially treated bacterial meningitis: If antibiotics were given prior to lumbar puncture
Additional CSF Parameters to Consider
- CSF protein level should be assessed (typically elevated in meningitis)
- CSF glucose level (typically decreased in bacterial meningitis)
- CSF lactate level (<2 mmol/L helps rule out bacterial disease) 2
- CSF Gram stain and culture are essential for identifying the causative organism
Correction Factors
- If there is blood in the CSF sample, correction factors may need to be applied
- The International Encephalitis Consortium recommends subtracting 1 WBC for every 700 RBCs in CSF 2
- This correction helps differentiate between true pleocytosis and contamination from a traumatic tap
Clinical Management Implications
Given the WBC count of 1,000 cells/μL and the clinical presentation:
- Immediate empiric antibiotic therapy is warranted
- Further diagnostic workup including blood cultures should be obtained
- Close monitoring for signs of increased intracranial pressure is essential
This CSF WBC count is significantly elevated and, in the context of the clinical presentation, requires urgent intervention to prevent morbidity and mortality associated with bacterial meningitis.