What are the diagnostic criteria and treatment options for a patient with suspected appendicitis?

Diagnostic Approach to Appendicitis

Use a risk-stratified approach combining clinical scoring systems (AIR or AAS scores in adults, Alvarado or Pediatric Appendicitis Score in children) with tailored imaging—ultrasound first for children and pregnant patients, CT with IV contrast for non-pregnant adults—to diagnose appendicitis and guide management decisions. 1

Initial Clinical Assessment and Risk Stratification

Begin by applying validated clinical scoring systems rather than relying on individual symptoms or signs, which have poor discriminatory power alone 1:

For Adults:

• Use the AIR (Appendicitis Inflammatory Response) score or AAS (Adult Appendicitis Score) as these are the best-performing clinical prediction tools with the highest discriminating power 1
• The AIR score performs better for men (cutoff ≤2, specificity 24.7%) while the AAS performs better for women (cutoff ≤8, specificity 63.1%) 1
• Do NOT use the Alvarado score alone to confirm appendicitis in adults due to insufficient specificity, though it helps exclude the diagnosis 1

For Children:

• Use the Alvarado score or Pediatric Appendicitis Score to exclude appendicitis 1
• Never make the diagnosis based on clinical scores alone in pediatric patients—imaging is required for confirmation 1

For Pregnant Patients:

• Do not rely on symptoms and signs alone 1
• Always request laboratory tests including CRP 1

Laboratory Testing

Obtain the following in all patients 1:

• White blood cell count with differential (absolute neutrophil count)
• C-reactive protein (CRP)

Key predictive values:

• In children: CRP ≥10 mg/L and leukocytosis ≥16,000/mL are strong predictive factors 1
• In all patients: The combination of WBC >10,000/mm³ AND CRP ≥8 mg/L has a positive likelihood ratio of 23.32 2
• Normal WBC and normal CRP together help exclude appendicitis 3

Imaging Strategy Based on Risk Category

Low-Risk Patients

• Discharge with 24-hour follow-up without imaging 1, 2
• No hospital admission or further testing needed 1

Intermediate-Risk Patients (Most Common Scenario)

Non-Pregnant Adults:

• CT abdomen and pelvis with IV contrast is the primary imaging modality 1, 2
• Sensitivity: 96-100%, Specificity: 93-95% 2, 4
• IV contrast is essential—increases sensitivity to 96% compared to unenhanced CT 2
• Oral contrast is NOT necessary and may delay diagnosis 2
• Consider low-dose CT with contrast in adolescents and young adults to reduce radiation exposure 1

Children and Adolescents:

• Ultrasound is the first-line imaging modality 1, 2
• Sensitivity: 76%, Specificity: 95% 2
• Key ultrasound findings: appendiceal diameter ≥7 mm, non-compressibility, appendiceal tenderness 2
• Point-of-care ultrasound (POCUS) by emergency physicians or surgeons shows higher accuracy: sensitivity 91%, specificity 97% 1, 2
• If ultrasound is non-diagnostic and clinical suspicion persists, proceed to MRI or low-dose CT 2

Pregnant Patients:

• Ultrasound is the initial imaging modality 1, 2
• If ultrasound is inconclusive, use MRI without IV contrast (NOT CT) 2
• MRI sensitivity: 94%, Specificity: 96% 1, 2

Elderly Patients:

• CT scan with IV contrast is strongly recommended due to higher rates of complicated appendicitis (55-70% perforation rate) and mortality 1, 2

High-Risk Patients

Adults <40 years with very high clinical suspicion (AIR score 9-12, Alvarado score 9-10, AAS ≥16):

• May proceed directly to surgery without preoperative imaging 1
• However, imaging should still be considered if clinical judgment conflicts with the high-risk stratification 1

Combined Clinico-Radiological Approach

Combine ultrasound findings with clinical scores to significantly improve diagnostic accuracy and reduce the need for CT 1, 2:

• This combined approach may eventually replace the need for CT in many adult patients 1
• Use POCUS as the most appropriate first-line diagnostic tool when imaging is indicated based on clinical assessment 1

CT Findings Indicating Complicated Appendicitis

The following CT findings suggest complicated appendicitis requiring urgent surgical intervention 1, 4:

• Extraluminal appendicolith
• Abscess formation
• Extraluminal air
• Appendiceal wall enhancement defect
• Periappendiceal fat stranding
• Appendiceal diameter >13 mm
• Mass effect

Patients with appendicolith, mass effect, or dilated appendix >13 mm have approximately 40% failure rate with antibiotics-first approach and should proceed to surgery if fit 4

Management After Inconclusive Imaging

If imaging is negative but clinical suspicion remains high 2:

• Consider observation with or without antibiotics
• Ensure 24-hour follow-up if discharged
• Surgical intervention if clinical suspicion is very high despite negative imaging
• Cross-sectional imaging is recommended before surgery for patients with normal investigations but non-resolving right lower quadrant pain 1

Common Pitfalls and Caveats

Ultrasound limitations 1, 2:

• Accuracy is highly operator-dependent
• Both MRI and ultrasound may incorrectly classify up to half of patients with perforated appendicitis as having simple appendicitis

Elderly patients 1, 2:

• Atypical presentations are common
• Higher mortality and morbidity rates
• Do not delay CT imaging due to radiation concerns—the need for accurate diagnosis outweighs radiation risk

Pregnant patients 1:

• Alvarado score can be falsely elevated due to higher WBC values and frequency of nausea/vomiting in first trimester
• Peritoneal signs may be less reliable due to anatomic displacement 2

Children <5 years 1:

• More frequently present with atypical symptoms
• Higher rate of perforated appendicitis due to delayed diagnosis
• Ultrasound is mandatory to avoid radiation exposure 1