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OBJECTIVE The American Association for the Surgery of Trauma (AAST) developed an anatomic grading system to assess disease severity through increasing grades of inflammation. Severity grading can then be utilized in risk-adjustment and stratification of patient outcomes for clinical benchmarking. We sought to validate the AAST appendicitis grading system by examining the ability of AAST grade to predict clinical outcomes used for clinical benchmarking. METHODS Surgical quality program data were prospectively collected on all adult patients undergoing appendectomy for acute appendicitis at our institution between December 2013 and May 2018. The AAST acute appendicitis grade from 1 to 5 was assigned for all patients undergoing open or laparoscopic appendectomy. Primary outcomes were occurrence of major complications, any complications, and index hospitalization length of stay. Multivariable models were constructed for each outcome without and with inclusion of the AAST grade as an ordinal variable. We also developed models using International Classification of Diseases, 9th or 10th Rev.—Clinical Modification codes to determine presence of perforation for comparison. RESULTS A total of 734 patients underwent appendectomy for acute appendicitis. The AAST score distribution included 561 (76%) in grade 1, 49 (6.7%) in grade 2, 79 (10.8%) in grade 3, 33 (4.5%) in grade 4, and 12 (1.6%) in grade 5. The mean age was 35.3 ± 14.7 years, 47% were female, 20% were nonwhite, and 69% had private insurance. Major complications, any complications, and hospital length of stay were all positively associated with AAST grade (p < 0.05). Risk-adjustment model fit improved after including AAST grade in the major complications, any complications, and length of stay multivariable regression models. The AAST grade was a better predictor than perforation status derived from diagnosis codes for all primary outcomes studied. CONCLUSION Increasing AAST grade is associated with higher complication rates and longer length of stay in patients with acute appendicitis. The AAST grade can be prospectively collected and improves risk-adjusted modeling of appendicitis outcomes. LEVEL OF EVIDENCE Prospective/Epidemiologic, Level III.

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