Is C-Reactive Protein (CRP) elevated in appendicitis?

CRP in Appendicitis

Yes, CRP is typically elevated in acute appendicitis, but normal CRP levels cannot reliably exclude the diagnosis, and elevated levels alone should not be used to confirm it.

Diagnostic Performance of CRP

CRP demonstrates good sensitivity but limited specificity for acute appendicitis:

• Sensitivity ranges from 77-93% for detecting acute appendicitis, meaning most patients with appendicitis will have elevated CRP 1, 2, 3
• Specificity is approximately 52-80%, indicating many patients without appendicitis may also have elevated CRP 2, 4
• The false-negative rate is approximately 3%, though up to 40% of patients with normal CRP and WBC may still have appendicitis 2, 4

CRP Levels Correlate with Disease Severity

CRP values increase with advancing inflammation:

• Mean CRP in normal appendix: 5 mg/L (range 0-12.6 mg/L) 2
• Mean CRP in non-perforated appendicitis: 33.8 mg/L (range 5-85.1 mg/L) 2
• Mean CRP in perforated appendicitis: 128.5 mg/L (range 79.2-230 mg/L) 2
• In elderly patients, CRP >101.9 mg/L suggests perforation (AUC 0.811) 1

Clinical Application Guidelines

CRP should be used as part of a comprehensive diagnostic approach, not in isolation:

• In pediatric patients, CRP ≥10 mg/L combined with leucocytosis ≥16,000/mL are strong predictive factors for appendicitis 1
• Guidelines strongly recommend routine laboratory tests including CRP in children with suspected appendicitis 1
• In elderly patients, elevated CRP cannot establish the diagnosis but should prompt appropriate imaging 1
• Normal CRP and leukocyte count in elderly patients had 100% negative predictive value in one series, though this finding requires validation 1

Critical Limitations

Important caveats when interpreting CRP:

• Normal inflammatory markers (including CRP) cannot rule out appendicitis, even with prolonged symptom duration 4
• 39.8% of patients with both normal CRP and WBC still had appendicitis in a large multicenter study 4
• CRP should be combined with clinical scoring systems (AIR, AAS) and imaging rather than used alone 1, 5
• The diagnosis must be guided by clinical judgment with CRP serving as an adjunct, not a definitive test 4

Timing Considerations

CRP elevation depends on symptom duration:

• Sensitivity and positive predictive value are highest within 48 hours of symptom onset (sensitivity 94%, PPV 0.87) 4
• Negative predictive value improves after 24 hours (NPV 0.65 at 24-48 hours vs 0.52 at <24 hours) 4
• CRP values increase with longer preoperative illness duration 6