HSAF
also known as: Hospital Service Area File
CMS's annual snapshot of where each hospital's patients come from — Medicare claims aggregated to ZIP-of-origin × hospital CCN.
The Hospital Service Area File (HSAF) is a CMS-published dataset that aggregates fee-for-service Medicare inpatient claims by hospital CCN × patient ZIP code of origin, for one calendar year at a time. It captures three metrics:
- Total cases (Medicare discharges from that ZIP to that hospital)
- Total days (Medicare inpatient days)
- Total charges (gross billed charges)
HSAF is the primary public-data source for "where do this hospital's patients come from" — a question every hospital strategist, ambulatory rollup buyer, and regulatory analyst needs to answer. It's especially useful for evaluating market share, catchment expansion, and competitive overlap between nearby hospitals.
Important caveats: HSAF reports only Medicare fee-for-service patients (no Medicaid, no commercial, no Medicare Advantage). And CMS suppresses any ZIP × CCN cell with <11 cases for patient-privacy protection — so HSAF is sparse in rural areas and for specialty hospitals.
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