ICD-9-and-10 Coding Transition Does Not Interfere with Trends in Aneurysmal Subarachnoid Hemorrhage Admissions in the United States

Introduction: The transition from ICD-9 to ICD-10 coding in 2015 has been a point of contention in analyses of large, public health databases, such as the National Inpatient Sample (NIS). Prior studies state that the transition is a source of bias and inconsistencies in longitudinal, population-based studies, especially those on cerebrovascular pathologies, and that future analyses should limit their scope to one coding system. This study aims to evaluate whether prevalence, demographic, and outcome trends for aneurysmal subarachnoid hemorrhage (aSAH) and its associated neurosurgical interventions were affected by the transition given recent studies on aSAH treatment that utilize both ICD-9-and-10 codes.

Methods: The NIS was queried for aSAH admissions from 2000-2020 and stratified by open surgical repair versus endovascular treatment using both ICD-9-and-10 codes. The annual prevalence of each intervention as well as the average age at admission and mortality rate were evaluated in a time series analysis using an autoregressive integrated moving average (ARIMA) linear spline model.

Results: From 2000-2020, the annual volume of open surgical repair decreased by an average of 342 cases (p < 0.001) while endovascular treatment increased by an average of 557 cases (p < 0.001). There were no disturbances in these annual trends relative to the coding transition in 2015 for either open repair (p=0.256) or endovascular treatment (p=0.209). The average age of admission steadily increased by 0.14 years (p < 0.001) while the mortality rate decreased by 0.2% (p=0.001) per year. These demographic (p=0.171) and outcome (p=0.061) trends were not distorted by the shift from ICD-9-to-10 coding.

Conclusion : With the proper ICD codes, analysis of aSAH can span both ICD-9-and-10 coding schemes without significant inaccuracies in cohort composition, demographics, and outcomes. These codes confirm trends in aSAH treatment, notably increased utilization of endovascular treatment, decreased use of open surgical repair, increased treatment of older patients, and improved outcomes following neurosurgical treatment.