Are erythrocyte sedimentation rate (ESR) and C‑reactive protein (CRP) usually elevated in acute meningitis?

Are ESR and CRP Usually Elevated in Acute Meningitis?

Yes, both ESR and CRP are typically elevated in acute bacterial meningitis, with CRP being more reliably and dramatically elevated than ESR. In bacterial meningitis, serum CRP is elevated in essentially all cases (96-100% sensitivity), while ESR is elevated in most but not all cases 1, 2, 3.

CRP in Acute Meningitis

CRP is the superior inflammatory marker for diagnosing bacterial meningitis, with serum levels >20 mg/L achieving 96% sensitivity, 93% specificity, and 99% negative predictive value 4. The evidence strongly supports CRP as the primary inflammatory marker:

• All patients with bacterial meningitis demonstrate markedly elevated serum CRP levels, regardless of illness duration, patient age, causative organism, fever presence, or CSF cell count 3
• CRP rises within 6 hours of acute inflammation and is secreted by the liver in response to bacterial infection 1
• Serum CRP concentrations distinguish bacterial from viral meningitis with an odds ratio of 150 (95% CI: 44-509) 1
• In viral meningitis, CRP is typically normal or only slightly elevated (mean 1.92 mg% vs. 8.78 mg% in bacterial meningitis) 2

Diagnostic Thresholds for CRP

• CRP >20 mg/L strongly suggests bacterial meningitis with 96% sensitivity and 93% specificity 4
• CRP <2 mg/dL measured at least 12 hours after fever onset makes bacterial meningitis far less likely 5
• CSF CRP >100 µg/L was present in all bacterial meningitis cases but only 10% of viral meningitis cases 6

ESR in Acute Meningitis

ESR is elevated in most cases of acute bacterial meningitis but is less specific and less reliable than CRP 2. The evidence shows:

• ESR demonstrates statistically significant differences between bacterial and viral meningitis (p <0.01) 2
• ESR is less useful than CRP because it is affected by multiple confounding factors including anemia, female sex, advanced age, and azotemia 7, 8
• ESR rises and falls more slowly than CRP, making it less responsive to acute changes in inflammation 7, 8

Clinical Algorithm for Using These Markers

When evaluating suspected meningitis, prioritize serum CRP over ESR for the following reasons:

1. Obtain serum CRP immediately upon suspicion of meningitis, ideally before antibiotic administration 1, 4

2. Interpret CRP in context with CSF parameters:

   • If CRP >20 mg/L AND any high-certainty CSF predictor is present (glucose <34 mg/dL, CSF:plasma glucose <0.23, protein >120 mg/dL, WBC >12,000/mm³, neutrophils >11,000/mm³), bacterial meningitis is virtually certain 4
   • A normal CRP (<20 mg/L) has high negative predictive value (99%) and may support withholding antibiotics in select cases with negative Gram stain 1, 4

3. ESR adds limited value beyond CRP and should not be used as the primary decision-making tool 7, 8

Critical Pitfalls to Avoid

• False-negative CRP results occur when measured too early (<12 hours after fever onset) 5
• Prior antibiotic treatment reduces the diagnostic accuracy of both markers, though CRP remains more reliable 2
• Never delay empiric antibiotics while awaiting inflammatory marker results if clinical suspicion is high 1, 4
• ESR may be artificially elevated by anemia, renal dysfunction, or female sex, reducing its specificity 7, 8
• Do not use inflammatory markers alone to determine whether to initiate antimicrobial therapy—they are adjunctive tests that must be interpreted with CSF analysis and clinical presentation 1

Monitoring Treatment Response

CRP is superior to ESR for monitoring treatment response because it normalizes within 7 days in uncomplicated bacterial meningitis, while ESR remains elevated longer 3, 9. Serial CRP measurements can detect complications such as subdural effusion or concurrent infections 3.