Can you code for bacterial meningitis if the diagnosis is only suspected based on lumbar puncture (LP) results?

Coding for Bacterial Meningitis Based on Lumbar Puncture Results

Bacterial meningitis should not be coded based solely on suspected diagnosis from lumbar puncture results; definitive diagnosis requires microbiological confirmation through CSF culture, Gram stain, or PCR. 1

Diagnostic Criteria for Bacterial Meningitis

• CSF analysis remains the principal contributor to the final diagnosis of bacterial meningitis, with CSF leukocyte count being the best diagnostic parameter (area under the curve of 0.95) 1
• Bacterial meningitis typically presents with:
  • Elevated CSF white blood cell count (usually 1000-5000 cells/mm³, but can range from 100-110,000 cells/mm³) 1
  • Neutrophil predominance (typically 80-95% of cells) 1
  • Low CSF glucose (<40 mg/dL in 50-60% of patients) 1
  • Low CSF:serum glucose ratio (<0.4 in adults) 1
  • Elevated CSF protein 1

Microbiological Confirmation Requirements

• Definitive diagnosis of bacterial meningitis requires microbiological confirmation through:

  • Positive CSF culture (positive in 70-85% of untreated patients) 1
  • Positive CSF Gram stain (60-90% sensitivity, 97% specificity) 1
  • Molecular diagnostic tests (PCR) when available 2

• The likelihood of visualizing bacteria on Gram stain correlates with CSF bacterial concentration:

  • 10³ CFU/mL: 25% positive rate
  • 10³-10⁵ CFU/mL: 60% positive rate

  • 10⁵ CFU/mL: 97% positive rate 1

Coding Implications

• Without microbiological confirmation (culture, Gram stain, or PCR), coding should reflect "suspected" or "possible" bacterial meningitis rather than definitive bacterial meningitis 3, 2
• CSF findings alone (pleocytosis, low glucose, high protein) can support a diagnosis of meningitis but cannot definitively distinguish bacterial from viral or other causes without microbiological confirmation 2
• In rare cases, bacterial meningitis can occur without CSF pleocytosis (124 documented cases), making microbiological confirmation even more critical for accurate diagnosis and coding 4

Timing Considerations

• CSF culture positivity decreases significantly after antibiotic administration:
  • 73% positive if LP performed within 4 hours of antibiotics
  • Only 11% positive if LP performed more than 4 hours after antibiotics
  • 0% positive if LP performed more than 8 hours after antibiotics 5

Best Practices

• When bacterial meningitis is suspected but microbiological confirmation is pending or negative:
  • Code for meningitis (unspecified) rather than bacterial meningitis 3, 2
  • Consider blood cultures as an adjunct diagnostic tool (positive in 71% of cases with bacterial meningitis without pleocytosis) 4
  • If clinical suspicion remains high despite initial negative results, consider repeat lumbar puncture, as meningitis can evolve over time 6

Common Pitfalls

• Coding for definitive bacterial meningitis based solely on CSF cell count, protein, and glucose without microbiological confirmation 2
• Failing to consider that prior antibiotic administration may reduce the yield of CSF cultures and Gram stain while still preserving other CSF abnormalities 2
• Not recognizing that bacterial meningitis can rarely present without CSF pleocytosis, especially in immunocompromised patients 4