Terminal Patients and the not so quite dead yet

This post is sort of piggy backing on the previous. Let's assume there is no family - just to keep them out of the picture.

Where exactly does the pt. get to say "No" to life saving treatment, and when is the line crossed when the hospital gets to say "Too bad, we've taken over."

For example, we have something called a DNR, and as far as I know, everyone can fill them out anywhere in the US. A DNR (Do Not Resuscitate) basically states if your heart stops beating, or you stop breathing, the hospital will not do anything like CPR, paddles, vent, etc. and as such, you will die shortly (Tho technically, if your heart stops, you are legally dead). Most (again, never all) people say you can fill out a DNR w/o any troubles.

Most would say you can refuse treatment if and when terminal in order to have quality instead of possible quantity of days. Metastatic, end stage cancer comes to mind and is a good example.

But how far down the tree can you go? What if moden medicine can treat it? Let's say you are diagnosed with an active tuberculosis (you can simply carry it around, and thus not have an "actice" infection). Let's also assume you won't be exposing your self to others in order to take out another factor. Do you have the right to refuse treatment that in all probability will lead to your death & where modern medicine can save your life?

I don't have a hard opinion on this, but its something to think about.