What are the steps to diagnose appendicitis?

How to Diagnose Appendicitis

Diagnostic imaging is now the standard for most patients with suspected acute appendicitis, with the exception of males under 40 years old who present with classic clinical findings. 1

Initial Clinical Assessment

Begin by evaluating for the classic symptom constellation, though recognize this appears in only ~50% of cases 2:

• Periumbilical pain migrating to the right lower quadrant (most helpful positive finding) 3, 4
• Anorexia, nausea, and vomiting (though vomiting before pain makes appendicitis unlikely) 3, 4
• Low-grade fever 3, 4
• Right lower quadrant tenderness with guarding 3, 5
• Positive psoas sign 3

Critical pitfall: Individual clinical signs have low predictive value, so never rely on clinical examination alone except in the narrow exception noted above. 1

Risk Stratification Using Clinical Scores

Use the AIR (Appendicitis Inflammatory Response) score or AAS (Adult Appendicitis Score) to stratify patients into low, intermediate, or high-risk categories. 1

These scores are superior to the older Alvarado score, which lacks sufficient specificity for positive diagnosis in adults. 1

• AIR score performs best in men (cutoff ≤2, specificity 24.7%) 1, 2
• AAS score performs best in women (cutoff ≤8, specificity 63.1%) 1, 2
• Low-risk patients can be discharged with 24-hour follow-up without imaging 1, 2
• Intermediate-risk patients require diagnostic imaging 1, 2
• High-risk patients may proceed directly to surgery based on clinical judgment 1

Laboratory Testing

Always obtain white blood cell count and C-reactive protein (CRP). 1, 2

The combination of normal WBC and normal CRP, combined with low clinical suspicion, helps exclude appendicitis. 1

In pregnant patients, laboratory tests and inflammatory markers are mandatory as clinical scores (including Alvarado) are less reliable due to physiologic changes. 1, 2

Diagnostic Imaging Algorithm

For Adult Males <40 Years with Classic Presentation

No imaging required - proceed based on clinical diagnosis. 1

For All Other Adults (Intermediate/High Risk)

CT abdomen/pelvis with IV contrast only (no oral or rectal contrast) is the imaging modality of choice. 1

• Sensitivity: 90-100%, Specificity: 94.8-100% 1, 2
• IV contrast alone is sufficient; oral contrast adds no diagnostic value and delays examination 1
• Helical CT technique is preferred 1

For Women of Childbearing Age

Obtain pregnancy test first. 1

• If pregnant (first trimester): Use ultrasound or MRI to avoid ionizing radiation 1, 2
• MRI has 96% sensitivity and specificity in pregnancy 2
• If ultrasound/MRI non-diagnostic, consider limited CT or diagnostic laparoscopy 1
• If not pregnant: Proceed with CT as above 1

For Pediatric Patients

Ultrasound is first-line imaging (sensitivity 51.8-81.7%, specificity 53.9-81.4%) 1, 2

• Imaging recommended for all children, particularly those <3 years old 1
• If ultrasound is non-diagnostic in intermediate-risk children, proceed to CT 1
• CT remains highly accurate in children (sensitivity ~94%, specificity ~95%) 1

Important limitation: Ultrasound has low sensitivity for perforated appendicitis, which matters if considering non-operative management. 1

Follow-Up for Negative Imaging

If imaging is negative but clinical suspicion persists, observe the patient in the emergency department or hospital. 1

• Mandatory 24-hour follow-up (even by telephone if discharged) due to measurable false-negative rates 1, 2
• Absence of improvement warrants re-examination, possible re-imaging, or diagnostic laparoscopy 1

Special Populations

Elderly Patients

Higher perforation rates (55-70%) and mortality, requiring lower threshold for imaging and surgical consultation. 2

HIV-Positive Patients

Alvarado score is less sensitive; maintain higher suspicion and lower threshold for imaging. 1

Pregnant Patients

Do not diagnose on symptoms alone; always obtain laboratory markers and appropriate imaging (ultrasound first, then MRI if needed). 1, 2