Validation of the Appendicitis Inflammatory Response (AIR) Score.

Background: Patients with suspicion of appendicitis present with a wide range of severity. Score-based risk stratification can optimise the management of these patients. This prospective study validates the Appendicitis Inflammatory Response (AIR) score in patients with suspicion of appendicitis.

Method: Consecutive patients over the age of five with suspicion of appendicitis presenting at 25 Swedish hospital's emergency departments were prospectively included. The diagnostic properties of the AIR score are estimated.

Results: Some 3878 patients were included, 821 with uncomplicated and 724 with complicated appendicitis, 1986 with non-specific abdominal pain and 347 with other diagnoses. The score performed better in detecting complicated appendicitis (ROC area 0.89 (95% confidence interval (CI) 0.88-0.90) versus 0.83 (CI 0.82-0.84) for any appendicitis, p < 0.001), in patients below age 15 years and in patients with >47 h duration of symptoms (ROC area 0.93, CI 0.90-0.95 for complicated and 0.87, CI 0.84-0.90 for any appendicitis in both categories). Complicated appendicitis is unlikely at AIR score <4 points (Negative Predictive Value 99%, CI 98-100%). Appendicitis is likely at AIR score >8 points, especially in young patients (positive predictive value (PPV) 96%, CI 90-100%) and men (PPV 89%, CI 84-93%).

Conclusions: The AIR score has high sensitivity for complicated appendicitis and identifies subgroups with low probability of complicated appendicitis or high probability of appendicitis. The discriminating capacity is high in children and patients with long duration of symptoms. It performs equally well in both sexes. This verifies the AIR score as a valid decision support. Trial registration number https://clinicaltrials.gov/ct2/show/NCT00971438.