How to define tribal communities in secondary data sets

Hello, I’m working with hospital discharge data and we are frequently asked to define data for tribal communities. The only way I know how to do that is to go down to the county or zip code level and then select everyone who said their race was Native American. Are there other ways of doing this that aren’t geography-based? This data isn’t collected by us so we can’t change the data types. I know we are painting an incomplete picture of tribal health so I wanted to get some other ideas that people might have.