How is appendicitis diagnosed?

Diagnostic Testing for Appendicitis

The diagnosis of appendicitis should begin with clinical risk stratification using signs, symptoms, and laboratory tests, followed by appropriate imaging based on patient characteristics, with CT being the preferred initial imaging modality for non-pregnant adults. 1, 2

Clinical Assessment and Risk Stratification

Key Clinical Findings

• Right lower quadrant pain
• Abdominal rigidity
• Periumbilical pain radiating to the right lower quadrant
• Rebound tenderness
• Nausea/vomiting
• Low-grade fever

Laboratory Tests

• White blood cell (WBC) count
  • Elevated WBC (>10,000/mm³) has a positive likelihood ratio of 2.47 1
  • WBC >15,000/mm³ has a higher positive likelihood ratio of 3.47 1
• C-reactive protein (CRP)
  • CRP >10 mg/L has a positive likelihood ratio of 4.24 1
  • Combined elevated WBC and CRP provides the strongest evidence (positive likelihood ratio of 23.32) 1

Risk Stratification Tools

• Alvarado Score - helps categorize patients into low, moderate, or high risk 3
  • Components: migration of pain, anorexia, nausea/vomiting, right lower quadrant tenderness, rebound pain, elevated temperature, leukocytosis, and left shift of neutrophils

Imaging Recommendations

For Non-Pregnant Adults

• First-line imaging: Abdominal CT scan 1, 2
  • Highest diagnostic accuracy (sensitivity 95%, specificity 94%) 2
  • Can identify alternative causes of abdominal pain
  • IV contrast is usually appropriate but CT without IV contrast also has high diagnostic accuracy 1
  • Reduced-dose CT protocols can minimize radiation exposure 2

For Pregnant Patients

• First-line imaging: Abdominal ultrasound 1, 2
  • Avoids radiation exposure
  • If ultrasound is equivocal, MRI is recommended as the second-line imaging modality 1, 2

For Children and Adolescents

• First-line imaging: Abdominal ultrasound 1, 2
  • Avoids radiation exposure
  • If initial ultrasound is equivocal/non-diagnostic, MRI is suggested as the subsequent imaging modality 1, 2

Important Considerations

Ultrasound Limitations

• Operator-dependent results
• Limited visualization in obese patients
• High rate of non-visualization of the appendix (up to 45%) 2
• Non-visualization should not be interpreted as absence of disease 2

When to Proceed Without Imaging

• Very low clinical suspicion: Consider discharge with minimal or no testing 1
• Very high clinical suspicion: Consider direct surgical consultation with minimal or no testing 1

Pitfalls to Avoid

• Relying solely on WBC count or CRP - these tests alone have limited predictive value 1
• Interpreting non-visualization of appendix on ultrasound as normal 2
• Delaying surgical consultation when clinical suspicion is high, as prolonged symptoms increase perforation risk 3
• Skipping imaging when diagnosis is uncertain, as clinical diagnosis alone has high rates of false positives and negatives 2

Algorithm for Suspected Appendicitis

1. Perform clinical assessment and laboratory tests (WBC, CRP)
2. Risk-stratify patient using clinical findings
3. Select appropriate imaging based on patient characteristics:
   • Non-pregnant adults: CT scan
   • Pregnant patients: Ultrasound → MRI if equivocal
   • Children: Ultrasound → MRI if equivocal
4. Obtain surgical consultation promptly if high clinical suspicion or positive imaging
5. Consider observation if low clinical suspicion and negative imaging

This approach balances diagnostic accuracy with radiation exposure considerations while prioritizing timely diagnosis to reduce the risk of perforation and associated morbidity and mortality.