What are the criteria for diagnosing acute appendicitis, including history, physical examination, laboratory findings, the Alvarado score, and imaging recommendations?

Diagnostic Criteria for Acute Appendicitis

Use the AIR score or Adult Appendicitis Score (AAS) in adults and the Alvarado score in children primarily to exclude appendicitis in low-risk patients, not to confirm the diagnosis. 1

Clinical Scoring Systems

Adults

• The AIR score and AAS score are the best-performing clinical prediction tools with the highest discriminating power in adults with suspected acute appendicitis. 1, 2

• Do not use the Alvarado score to confirm appendicitis in adults—it lacks sufficient specificity and is unreliable in elderly patients and those with HIV. 1

• Risk stratification by AIR score:

  • Low-risk (AIR 0-4): Appendicitis probability <5%; discharge with return precautions, no imaging needed 3
  • Intermediate-risk (AIR 5-8): Proceed with ultrasound first-line; if inconclusive, obtain CT with IV contrast 3
  • High-risk (AIR 9-12): Appendicitis probability 78-98%; patients <40 years may proceed directly to surgical consultation without pre-operative CT 1, 3

Pediatric Patients

• Use the Alvarado score or Pediatric Appendicitis Score (PAS) to exclude appendicitis and identify intermediate-risk patients, but never make the diagnosis based on scores alone. 1, 4, 2

• Routinely obtain white blood cell count with differential and CRP in all children with suspected appendicitis. 1, 4

• CRP ≥10 mg/L and WBC ≥16,000/mL are strong predictive factors for appendicitis in pediatric patients. 1, 4

• Preschool-aged children often have lower scores even when appendicitis is present, making scoring systems less reliable in younger children. 4

History and Physical Examination

• Classic presentation includes: periumbilical pain migrating to the right lower quadrant, anorexia, nausea/vomiting, and low-grade fever—this constellation has approximately 90% diagnostic accuracy. 5

• Individual clinical variables have low predictive value, necessitating a tailored approach based on age, sex, and disease probability. 1

• In pregnant patients, never rely on symptoms and signs alone—always obtain laboratory tests and inflammatory serum parameters (CRP). 1

Laboratory Findings

• White blood cell count with differential (absolute neutrophil count) and CRP are the most useful laboratory tests. 1, 4

• In children specifically: CRP ≥10 mg/L and leucocytosis ≥16,000/mL strongly predict appendicitis. 1, 4

Imaging Recommendations

First-Line Imaging

• Point-of-care ultrasound (POCUS) or formal ultrasound is the recommended first-line imaging in both adults and children when imaging is indicated based on clinical assessment. 1, 4

• Combine ultrasound with clinical parameters (including scores) to significantly improve diagnostic sensitivity and specificity and reduce the need for CT. 1

Advanced Imaging

• For intermediate-risk patients with negative or inconclusive ultrasound: proceed to contrast-enhanced low-dose CT scan. 1, 4

• Contrast-enhanced low-dose CT should be preferred over standard-dose CT for adolescents and young adults. 1

• High-risk CT findings associated with treatment failure (if considering non-operative management) include: appendicolith, mass effect, and appendiceal diameter >13 mm. 5

Special Populations

• In pregnant patients: graded compression trans-abdominal ultrasound is the preferred initial method; if inconclusive, MRI is highly specific but a negative MRI does not exclude appendicitis. 1

• In pediatric patients: ultrasound is accurate and safe as first-line imaging. 1, 4

Diagnostic Algorithm

1. Calculate clinical score (AIR/AAS in adults, Alvarado/PAS in children) and obtain WBC with differential and CRP. 1, 4, 2

2. Low-risk patients: Discharge with return precautions, no imaging required. 3

3. Intermediate-risk patients: Proceed with ultrasound; if inconclusive and clinical suspicion persists, obtain CT. 1, 3

4. High-risk patients <40 years with AIR 9-12 or Alvarado 9-10: May proceed directly to surgical consultation without pre-operative imaging. 1

5. Patients with normal investigations but non-resolving right iliac fossa pain: Cross-sectional imaging is recommended before surgery. 1

Critical Pitfalls

• Never use the Alvarado score to confirm appendicitis in adults—it is only useful for exclusion. 1, 2

• Clinical scores alone over-diagnose appendicitis by 32-35% in pediatric patients. 1

• The final decision must incorporate clinical judgment from an experienced surgeon, especially in preschool-aged children where scores are less reliable. 4

• In elderly patients, scoring systems may be less reliable due to atypical presentations. 3