Medical expenses are really outrageous. The initial bill will show the amount due if you had no insurance. Blue Cross negotiates rates with hospitals, based on the treatment, tests, diagnosis, and probably some other variables. Your stay was in whatever category that pays $2,800. You are lucky. If you had no insurance, you would be responsible for the entire $8,500.
Prices are continually going up to balance out the small payments from Medicare and managed care (what you have). It's all a bit of a mess, in my opinion.
It's good that it wasn't a heart attack. So what are you doing as a result of all these tests? I hope you do something and get all the numbers down...
Sue