Defining Referral Regions for Inpatient Trauma Care: The Utility of a Novel Geographic Definition.

Abstract

Geographic variation is an inherent feature of the US health system. Despite efforts to account for geographic variation in trauma system strengthening, it remains unclear how trauma "regions" should be defined. The objective of this study is to evaluate the utility of a novel definition of Trauma Referral Regions (TRR) for assessing geographic variation in inpatient trauma across the age span of hospitalized trauma patients. Using 2016-2017 State Inpatient Databases, we assessed the extent of geographic variability in three common metrics of hospital use (localization index, market share index, net patient flow) among TRRs and, as a comparison, trauma regions alternatively defined based on Hospital Referral Regions, Hospital Service Areas, and counties. A total of 860,593 admissions from 102 TRRs, 127 Hospital Referral Regions, 884 Hospital Service Areas, and 583 counties were included. Consistent with expectations for distinct trauma regions, TRR presented with high average localization indices (mean [standard deviation]: 83.4 [11.7%]), low market share indices (mean [standard deviation]: 11.9 [7.0%]), and net patient flows close to 1.00. Similar results were found among stratified pediatric, adult, and older adult patients. Associations between TRRs and variations in important demographic features (e.g., travel time by road to the nearest Level I or II Trauma Center) suggest that while indicative of standalone trauma regions, TRRs are also able to simultaneously capture critical variations in regional trauma care. TRRs offer a standalone set of geographic regions with minimal variation in common metrics of hospital use, minimal geographic clustering, and preserved associations with important demographic factors. They provide a needed, valid means of assessing geographic variation among trauma systems.