Appendicitis Inflammatory Response (AIR) Score
Diagnoses acute appendicitis using clinical and laboratory findings
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Why use it
Provides better diagnostic accuracy than the Alvarado score by incorporating CRP and graded rebound tenderness. The AIR score has higher sensitivity and specificity for identifying advanced appendicitis (perforation, abscess). It reduces negative appendectomy rates and unnecessary CT imaging in low-risk patients.
About
The Appendicitis Inflammatory Response (AIR) Score is a validated clinical prediction rule for diagnosing acute appendicitis. It combines clinical findings (vomiting, RIF pain, rebound tenderness/muscular defense, elevated temperature) with laboratory inflammatory markers (polymorphonuclear leukocytes, WBC, CRP) to stratify patients into low, intermediate, and high probability groups. The AIR score was specifically designed to incorporate CRP — a late but highly specific marker — making it more accurate than the Alvarado score, particularly at identifying high-risk patients who need urgent surgery.
When to use
- Adults and adolescents presenting with acute right iliac fossa pain suspicious for appendicitis
- Stratifying patients before CT or ultrasound imaging decisions
- Emergency department triage for suspected acute appendicitis
- Post-imaging risk reassessment with inflammatory markers
Formula
Pearls & pitfalls
- CRP is the most specific single marker for advanced appendicitis (perforation, abscess); it is included in AIR but not in Alvarado.
- Rebound tenderness/muscular defense is graded (mild=1, moderate=2, strong=3) — not binary as in Alvarado.
- A score of 0–4 has a negative predictive value >95% for appendicitis in multiple validation studies.
- AIR ≥ 9 has a positive predictive value >90% for advanced or perforated appendicitis.
- In women of childbearing age, always exclude gynecological causes (ectopic pregnancy, ovarian torsion, PID) regardless of AIR score.
- CRP may be normal in early appendicitis (within first 6-12 hours of symptom onset) — repeat labs if clinical suspicion remains.
- The AIR score has been validated prospectively in Swedish, UK, and Asian populations.
Next steps
Low risk (AIR 0–4): Appendicitis unlikely — discharge with return precautions or observe; imaging at clinician discretion. Intermediate risk (AIR 5–8): Active in-hospital observation, serial abdominal exams, CT abdomen/pelvis or ultrasound recommended. High risk (AIR 9–12): High probability of appendicitis — urgent surgical consultation; imaging if it will not delay surgery.
Evidence
Andersson M & Andersson RE (World J Surg 2008) derived the AIR score from 545 patients. Prospective validation demonstrated AUC 0.97 for advanced appendicitis. Subsequent external validations across Europe and Asia confirm sensitivity 96% and specificity 97% at the high-risk threshold. Outperforms Alvarado score in discriminating advanced appendicitis.