What it is
The Appendicitis Inflammatory Response (AIR) score, derived by Andersson, risk-stratifies suspected acute appendicitis using symptoms, signs and three inflammatory markers (WBC, polymorph fraction, CRP). It runs 0–12 and was designed to sort patients into outpatient follow-up, active observation/imaging, or surgical review — outperforming the Alvarado score in most head-to-head series.
The criteria
Several items are graded rather than yes/no:
| Item | Points |
|---|---|
| Vomiting | +1 |
| Right iliac fossa pain | +1 |
| Rebound tenderness / guarding — light / medium / strong | +1 / +2 / +3 |
| Temperature ≥38.5°C | +1 |
| Polymorphs — 70–84% / ≥85% | +1 / +2 |
| WBC — 10–14.9 / ≥15 (×10⁹/L) | +1 / +2 |
| CRP — 10–49 / ≥50 (mg/L) | +1 / +2 |
Maximum 12. Note the graded rebound/guarding (up to +3) and the use of CRP, which Alvarado lacks.
Interpretation bands
- 0–4 — low probability. Outpatient follow-up is reasonable.
- 5–8 — indeterminate. Active in-hospital observation with re-scoring, or diagnostic imaging.
- 9–12 — high probability. Surgical review/exploration.
At the high cutoff (≥9) specificity is excellent (~97% in meta-analysis) but sensitivity is low — a high score rules in, a low score helps rule out, and the middle band is exactly where imaging earns its place.
When to use it
In the patient with suspected appendicitis where you want a more discriminating stratifier than Alvarado, particularly to support non-operative observation of the indeterminate group and to spare low-risk patients imaging. In children, pair it with the Pediatric Appendicitis Score (PAS), which is the more paediatric-validated tool; use AIR alongside serial examination.
Worked example
A 15-year-old: vomiting (+1), RIF pain (+1), medium guarding (+2), temperature 38.7°C (+1), polymorphs 88% (+2), WBC 16 ×10⁹/L (+2), CRP 60 mg/L (+2).
Total = 11/12 → high probability. Surgical review is warranted; the score complements, not replaces, examination and imaging where indicated.
Pitfalls
- Low sensitivity at the high cutoff — do not interpret a non-high score as “not appendicitis”; serial exam still rules.
- The indeterminate band is large and is the intended target for observation/imaging, not for discharge.
- Requires CRP and a differential WBC — the score is incomplete without bloods.
- Grade rebound/guarding honestly; over-calling “strong” inflates the score.
- Better specificity than Alvarado in many series, but still a decision aid — not a substitute for surgical assessment or imaging.
Run it: Appendicitis Inflammatory Response (AIR) Score
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.