A proposed method for identifying Interfacility transfers in Medicare claims data

To develop a method of consistently identifying interfacility transfers (IFTs) in Medicare Claims using patients with ST-Elevation Myocardial Infarction (STEMI) as an example. 100% Medicare inpatient and outpatient Standard Analytic Files and 5% Carrier Files, 2011-2020. Observational, cross-sectional comparison of patient characteristics between proposed and existing methods. We limited to patients aged 65+ with STEMI diagnosis using both proposed and existing methods. We identified 62,668 more IFTs using the proposed method (86,128 versus 23,460). A separately billable interfacility ambulance trip was found for more IFTs using the proposed than existing method (86% vs. 79%). Compared with the existing method, transferred patients under the proposed method were more likely to live in rural (p < 0.001) and lower income (p < 0.001) counties and were located farther away from emergency departments, trauma centers, and intensive care units (p < 0.001). Identifying transferred patients based on two consecutive inpatient claims results in an undercount of IFTs and under-represents rural and low-income patients.