Backgrounds
Patients presenting with suspected appendicitis pose a diagnostic challenge. The Appendicitis Inflammatory Response (AIR) score has out-performed the Alvarado score in two retrospective studies. The aim of this study was to prospectively evaluate the AIR Score and compare its performance in predicting risk of appendicitis to both the Alvarado score and the clinical impression of a senior surgeon.

Materials and Methods
All parameters included in the AIR and Alvarado scores as well as the initial clinical impression of a senior surgeon were prospectively recorded on patients referred to the surgical on call team with acute right iliac fossa pain over a 6-month period. Predictions were correlated with the final diagnosis of appendicitis.

Results
Appendicitis was the final diagnosis in 67 of 182 patients (37%). The three methods of assessment stratified similar proportions (~40%) of patients to a low probability of appendicitis (p=0.233) with a false negative rate of <8% that did not differ between the AIR score, Alvarado score or clinical assessment. The Alvarado score assigned the highest proportion of patients to the high probability of appendicitis group (45%, p<0.001). A high AIR score was associated with high specificity (97%) and positive predictive values (88%) but a specificity (33%) that was lower than the Alvarado score (80%) or surgical assessment (63%).

Conclusion
The AIR score is accurate at excluding appendicitis in those deemed low risk and in predicting it in those deemed high risk. Its use as the basis for selective CT imaging in those deemed medium risk should be considered.