A Multicenter Assessment of the Accuracy of Claims Data in Appendicitis Research

To investigate the accuracy of International Classification of Disease (ICD)-9/10 billing codes in a multicenter cohort.

Health services research on appendicitis often relies on administrative databases. However, billing codes may misclassify disease severity, as we demonstrated previously in a single institution study.

We performed a multicenter study of adult patients with appendicitis who presented to one of 6 US medical centers from 2012 to 2015 (ICD-9 era) and 2018 to 2021 (ICD-10 era). Patients were identified based on ICD codes. The diagnosis was confirmed via chart review. Each patient was characterized as complicated or uncomplicated based on AAST criteria; this was considered the gold standard. Billing codes were compared to the gold standard to calculate test parameters (ie, sensitivity).

In total, 1832 patients met the inclusion criteria. A total of 54.1% were male, 25% non-White, and 44% publicly insured or uninsured. In total, 21.1% of patients had complicated appendicitis based on the gold standard: 18.8% (312/1661) of surgical patients and 43.9% (75/171) of nonoperative patients ( P <0.001). Among all patients, 17.3% had a billing code for complicated appendicitis (12.5% true positives and 4.8% false positives). A total of 40.8% (158 of 387) of patients with complicated appendicitis were misclassified as having uncomplicated appendicitis via ICD codes. Sensitivity and PPV for complicated appendicitis were 0.59 (95% CI: 0.54-0.64) and 0.72 (95% CI: 0.67-0.77), respectively.

Billing codes have poor sensitivity and PPV for distinguishing complicated from uncomplicated appendicitis. These results have significant implications for how we should interpret data from administrative database studies and construct future analyses. Inaccuracies in billing codes negatively impact hospital reimbursement, with a tendency toward underpayment.