KEY_NASS is an HCUP record identifier created specifically for the NASS. Its purpose is to uniquely identify records so that the data elements from different NASS files can be combined. KEY_NASS does not link to other HCUP databases or to external databases.

KEY_NASS is a unique record identifier and cannot be used to track a person over time.

Prior to data year 2023, the first digit of KEY_NASS identifies the Census region. Starting in data year 2023, information on Census region is excluded.