Laboratory Testing Findings in Appendicitis
The most reliable laboratory findings for diagnosing appendicitis include elevated white blood cell count (>10,000/mm³), increased neutrophil percentage (>75%), and elevated C-reactive protein (CRP), with the combination of all three tests providing the highest diagnostic accuracy (sensitivity 95.3%, specificity 72.2%). 1, 2
Key Laboratory Markers
White Blood Cell (WBC) count is frequently elevated (>10,000/mm³) in acute appendicitis with a sensitivity of 75-77.5% and specificity of 63%, though a normal WBC count does not reliably exclude appendicitis 3, 1, 2
Neutrophil percentage (NP) >75% or neutrophil shift to the left is the most sensitive individual marker (82% sensitivity, 63% specificity) and should be evaluated in all suspected cases 4, 1
C-reactive protein (CRP) is the most specific individual marker (67% specificity, 76% sensitivity) and its level correlates with the severity of inflammation, with higher values suggesting perforation or abscess formation 1, 2
Diagnostic Value of Combined Testing
When all three markers (WBC, neutrophil count, and CRP) are normal, acute appendicitis can be excluded with a 100% negative predictive value 5
The combination of elevated WBC, elevated neutrophil count, or elevated CRP demonstrates a significantly improved sensitivity of 96% for diagnosing appendicitis 1
In patients with triple positive tests (elevated WBC, neutrophil count, and CRP), 95.2% had confirmed appendicitis 2
Special Considerations
Laboratory tests alone are insufficient for diagnosis and should be used in conjunction with clinical assessment and imaging studies 4, 6
The Appendicitis Inflammatory Response (AIR) score, which incorporates CRP values, has better diagnostic accuracy than the older Alvarado score 4
In elderly patients, laboratory tests have limited diagnostic accuracy, but unelevated WBC and CRP values together can exclude appendicitis with a 100% negative predictive value 4
A high CRP value (>101.9 mg/l) in elderly patients may suggest perforation 4
Early appendicitis may not yet demonstrate laboratory abnormalities, so normal lab values should not rule out appendicitis when clinical suspicion exists 3
Clinical Application
Laboratory tests should be used to risk-stratify patients and guide decisions about further testing and management 6
Patients with intermediate risk based on clinical scores and laboratory values should undergo timely and systematic diagnostic imaging 4
Do not base the diagnosis of acute appendicitis solely on laboratory values, especially in pregnant patients and elderly individuals 4, 3
CRP levels are particularly useful for identifying complicated appendicitis (perforation or abscess formation) and should be monitored to assess disease severity 2, 5