How does a doctor determine COPD staging?

Hi sandie, and thanks for this excellent question. We cannot speak on behalf of all physicians, but there is a pretty standardized system that is used for the staging of COPD.
I thought this article, by our own Theresa Cannizzaro, would provide you with a good description of the staging and the standard, too: https://copd.net/clinical/new-to-staging/.
I do hope you find it to be helpful.
All the best, Leon (site moderator)