Appendicitis Inflammatory Response (AIR) score
Probability of acute appendicitis from clinical signs, WBC, neutrophils and CRP
- WSES Jerusalem guidelines 2020
Sources last checked: 2026-10-13
Appendicitis Inflammatory Response (AIR) score
Probability of acute appendicitis from clinical signs, WBC, neutrophils and CRP
Derived in Swedish hospitals in patients admitted with suspected appendicitis. Rebound/guarding grading is subjective. In pregnancy, children and the elderly the score performs less well; WSES advises against diagnosing appendicitis in children or pregnant women on a score alone.
Interpretation
| 0–4 — low probability | WSES 2020 states that low-risk patients can be spared imaging and, if the clinical picture allows, discharged with safety-netting advice, with reassessment if symptoms persist. |
|---|---|
| 5–8 — indeterminate | Indeterminate zone: the score alone neither confirms nor excludes appendicitis. Approaches described for this group include active observation with repeat scoring, imaging (ultrasound, low-dose CT) or diagnostic laparoscopy, depending on local practice. |
| 9–12 — high probability | WSES 2020: in high-risk patients younger than 40, pre-operative cross-sectional imaging may be omitted before diagnostic ± therapeutic laparoscopy. |
What is the Appendicitis Inflammatory Response (AIR) score?
The Appendicitis Inflammatory Response (AIR) score combines clinical findings with WBC, neutrophil proportion and CRP to estimate the probability of acute appendicitis. Manne and Roland Andersson derived it in 2008 from 545 patients admitted with suspected appendicitis to four Swedish hospitals. The WSES Jerusalem guideline 2020 rates it among the best-performing clinical scores.
When to use it
- Adults with right lower abdominal pain and suspected appendicitis in the emergency department.
- Deciding between discharge, observation with imaging, or surgical exploration.
- Reducing unnecessary imaging and negative appendicectomies in low-risk patients.
When not to use it
- As the only basis for diagnosis in pregnant women or children.
- Patients with generalised peritonitis or haemodynamic instability — outside the situation the score was designed for.
How it is calculated
| Criterion | Points |
|---|---|
| Vomiting | +1 |
| Pain in the right inferior fossa | +1 |
| Rebound tenderness or muscular defence | |
| None | 0 |
| Light | 1 |
| Medium | 2 |
| Strong | 3 |
| Body temperature ≥ 38.5 °C | +1 |
| Polymorphonuclear leukocytes (neutrophils) | |
| < 70 % | 0 |
| 70–84 % | 1 |
| ≥ 85 % | 2 |
| WBC count | |
| < 10.0 × 10⁹/L | 0 |
| 10.0–14.9 × 10⁹/L | 1 |
| ≥ 15.0 × 10⁹/L | 2 |
| CRP | |
| < 10 mg/L | 0 |
| 10–49 mg/L | 1 |
| ≥ 50 mg/L | 2 |
Clinical pearls and limitations
- Derived in Swedish hospitals in patients admitted with suspected appendicitis. Rebound/guarding grading is subjective. In pregnancy, children and the elderly the score performs less well; WSES advises against diagnosing appendicitis in children or pregnant women on a score alone.
- Unlike Alvarado, it grades rebound tenderness and lab values, and includes CRP.
- WSES 2020 recommends the AIR and Adult Appendicitis Score as clinical predictors (strong recommendation).
- A score of 5–8 is the indeterminate zone: on its own it neither supports discharge nor confirms appendicitis.
- Some later studies used ≤ 3 instead of ≤ 4 as the low-risk cut-off; this calculator uses the original bands.
Frequently asked questions
What AIR score means appendicitis is unlikely?
0–4 points: low probability; WSES 2020 states that such patients can often be spared imaging and discharged with safety-netting advice if the clinical picture fits.
Is the AIR score better than Alvarado?
In the derivation study its ROC area was higher (0.93 vs 0.88 for all appendicitis) and WSES prefers it for adults.
Which CRP unit does the AIR score use?
mg/L. If your laboratory reports mg/dL, multiply by 10.
Evidence and guidelines
- Primary source: Andersson M, Andersson RE. The appendicitis inflammatory response score: a tool for the diagnosis of acute appendicitis that outperforms the Alvarado score. World J Surg 2008;32(8):1843-1849.
- Di Saverio S et al. Diagnosis and treatment of acute appendicitis: 2020 update of the WSES Jerusalem guidelines. World J Emerg Surg 2020;15:27 (statements 1.2–1.10).
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<p><a href="https://medelix.ai/en/calculators/air-score-appendicitis">Appendicitis Inflammatory Response (AIR) score calculator by Medelix</a></p>For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.