What are the initial labs and treatment for suspected meningitis?

Initial Labs and Treatment for Suspected Meningitis

In suspected meningitis, blood cultures should be obtained immediately, followed by lumbar puncture within 1 hour of hospital arrival (if safe), and empiric antibiotics should be started within the first hour after obtaining these specimens.

Initial Assessment and Stabilization

1. Stabilize airway, breathing, and circulation as immediate priority 1
2. Document Glasgow Coma Scale (GCS) score 1
3. Assess for signs of shock or severe sepsis
4. Determine need for senior review and/or intensive care admission within the first hour 1

Diagnostic Workup

Blood Tests (obtain within 1 hour of arrival)

• Blood cultures (essential before antibiotics) 1
• Complete blood count with differential
• Blood glucose (critical for CSF/blood glucose ratio interpretation) 2, 3
• Serum electrolytes
• Renal and liver function tests
• Coagulation studies

Lumbar Puncture

• Perform within 1 hour of arrival if safe to do so 1
• Indications for neuroimaging before LP: 1
  • Focal neurological signs
  • Presence of papilledema
  • Continuous or uncontrolled seizures
  • GCS ≤ 12

CSF Analysis

Basic tests to be performed on all CSF samples: 1

• Cell count with differential
• Glucose and protein concentrations
• CSF/blood glucose ratio (optimal cutoff ≤0.36, sensitivity 92.9%, specificity 92.9%) 2
• Gram stain
• Bacterial culture

Suggestive CSF findings for bacterial meningitis: 1, 4

• CSF glucose ≤35 mg/dL
• CSF/blood glucose ratio ≤0.4
• CSF protein ≥220 mg/dL
• CSF WBC ≥2,000/μL or neutrophils ≥1,180/μL

Treatment Algorithm

For Suspected Meningitis WITHOUT Signs of Shock or Severe Sepsis:

1. Obtain blood cultures
2. Perform LP within 1 hour if safe
3. Start antibiotics immediately after LP and within the first hour 1
4. If LP cannot be performed within 1 hour or is delayed for neuroimaging, start antibiotics immediately after blood cultures 1

For Patients with Predominantly Sepsis or Rapidly Evolving Rash:

1. Obtain blood cultures immediately
2. Start antibiotics immediately after blood cultures
3. Begin fluid resuscitation with initial 500 mL crystalloid bolus 1
4. Defer LP until patient is stabilized 1

Empiric Antibiotic Therapy

Adults:

• First-line: Ceftriaxone 2g IV every 12-24 hours (not to exceed 4g daily) 5 PLUS
• Vancomycin (if prevalence of ceftriaxone-resistant S. pneumoniae exceeds 1%) 4
• Add Ampicillin 2g IV every 4 hours for patients >50 years, immunocompromised, or if Listeria is suspected 6, 4

Pediatric Patients with Meningitis:

• Initial dose: 100 mg/kg of ceftriaxone (not to exceed 4 grams) 5
• Thereafter: 100 mg/kg/day (not to exceed 4 grams daily) 5

Adjunctive Therapy:

• Dexamethasone should be administered with or just before first antibiotic dose 4
• Discontinue dexamethasone if Listeria monocytogenes is confirmed 4

Important Pitfalls to Avoid

1. Delaying antibiotics: If LP is delayed for any reason (including neuroimaging), start empiric antibiotics immediately after blood cultures 1

2. Misinterpreting CSF results after antibiotics: The yield of CSF cultures and Gram stain may be diminished by prior antibiotics, but CSF cell count, glucose, and protein abnormalities will likely persist 1

3. Overlooking the CSF/blood glucose ratio: This may be the most precise single indicator for bacterial meningitis (more accurate than absolute CSF glucose) 2

4. Neglecting special populations: Older adults and immunocompromised patients require broader coverage including Listeria (add ampicillin) 4

5. Failing to recognize contraindications to immediate LP: Patients with focal neurological signs, papilledema, seizures, or GCS ≤12 should have neuroimaging first 1