Abstract
ImportanceAt the turn of the 21st century, studies evaluating the change in incidence of appendicitis over time have reported inconsistent findings.ObjectivesWe compared the differences in the incidence of appendicitis derived from a pathology registry versus an administrative database in order to validate coding in administrative databases and establish temporal trends in the incidence of appendicitis.DesignWe conducted a population-based comparative cohort study to identify all individuals with appendicitis from 2000 to2008.Setting & ParticipantsTwo population-based data sources were used to identify cases of appendicitis: 1) a pathology registry (n = 8,822); and 2) a hospital discharge abstract database (n = 10,453).Intervention & Main OutcomeThe administrative database was compared to the pathology registry for the following a priori analyses: 1) to calculate the positive predictive value (PPV) of administrative codes; 2) to compare the annual incidence of appendicitis; and 3) to assess differences in temporal trends. Temporal trends were assessed using a generalized linear model that assumed a Poisson distribution and reported as an annual percent change (APC) with 95% confidence intervals (CI). Analyses were stratified by perforated and non-perforated appendicitis.ResultsThe administrative database (PPV = 83.0%) overestimated the incidence of appendicitis (100.3 per 100,000) when compared to the pathology registry (84.2 per 100,000). Codes for perforated appendicitis were not reliable (PPV = 52.4%) leading to overestimation in the incidence of perforated appendicitis in the administrative database (34.8 per 100,000) as compared to the pathology registry (19.4 per 100,000). The incidence of appendicitis significantly increased over time in both the administrative database (APC = 2.1%; 95% CI: 1.3, 2.8) and pathology registry (APC = 4.1; 95% CI: 3.1, 5.0).Conclusion & RelevanceThe administrative database overestimated the incidence of appendicitis, particularly among perforated appendicitis. Therefore, studies utilizing administrative data to analyze perforated appendicitis should be interpreted cautiously.
Highlights
The appendectomy for appendicitis is the most commonly performed emergency abdominal operation conducted in North America
The incidence of appendicitis significantly increased over time in both the administrative database (APC = 2.1%; 95% CI: 1.3, 2.8) and pathology registry (APC = 4.1; 95% CI: 3.1, 5.0)
The administrative database overestimated the incidence of appendicitis, among perforated appendicitis
Summary
The appendectomy for appendicitis is the most commonly performed emergency abdominal operation conducted in North America. [6,7,8,9,10] These studies have used discharge abstract databases that code appendicitis based on the International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) or the Tenth Revision (ICD-10-CA).[11, 12] Reliance on ICD codes to identify cases with appendicitis introduces the potential for a misclassification error because approximately 12% of appendectomies remove a normal appendix.[13] This error can potentially be compounded when codes are used to differentiate appendicitis into perforated versus non-perforated appendicitis. Misclassification of ICD codes may result in misreporting of the incidence of appendicitis and possibly incorrect conclusions when assessing temporal trends of incidence.[14] These issues are negated when a pathology-proven registry of appendicitis cases are used; pathology reports are not available for research in most jurisdictions and compiling this data is time- and cost-inefficient
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