Power Has Pitfalls: (In)accuracy of Administrative Data for Nonoperative Management of Appendicitis

Introduction: Nonoperative management (NOM) of uncomplicated appendicitis is increasingly common. Effectiveness of NOM has been studied by identifying patients via International Classification of Diseases (ICD) 9/ICD-10 codes for uncomplicated appendicitis and no code for appendectomy. We sought to assess the accuracy of such administrative definitions.

Methods: We retrospectively identified patients with ICD-9/ICD-10 codes for appendicitis at five sites across the United States. Initial management plan and clinical severity were recorded by trained abstractors. We identified a gold standard cohort of patients with surgeon-diagnosed uncomplicated appendicitis and planned NOM. We defined two administrative cohorts with ICD-9/ICD-10 codes for uncomplicated appendicitis and either no surgery during initial admission (definition #1) or no surgery on day 0-1 of admission (definition #2). We compared each definition to the gold standard.

Results: Among 1224 patients with uncomplicated appendicitis, 72 (5.9%) underwent planned NOM. NOM patients were older (median [Q1-Q3] of 37 [27-56] versus 32 [25-44] y) and less frequently male (51.4% versus 54.9%), White (54.1% versus 67.6%), and privately insured (38.9% versus 50.2%) than patients managed operatively. Definition #1 had sensitivity of 0.81 and positive predictive value of 0.87 for NOM of uncomplicated appendicitis. Definition #2 had sensitivity of 0.83 and positive predictive value of 0.72. The gold standard cohort had a true failure/recurrence rate of 23.6%, compared with apparent rates of 25.4% and 39.8%, respectively.

Conclusions: Administrative definitions are prone to misclassification in identifying planned NOM of uncomplicated appendicitis. This likely impacts outcomes in studies using administrative databases. Investigators should disclose how misclassification may affect results and select an administrative definition that optimally balances sensitivity and specificity for their research question.