The other side of that is that there are many non-Alzheimer's causes of dementia in elderly patients. If a patient has dementia symptoms (along with a bunch of other problems) it can be really difficult for doctors to diagnose the root cause. For example my grandma's mental capacity was slowly deteriorating and they eventually determined it was because her bone marrow wasn't producing enough red blood cells, thus reducing the oxygen supply to her brain.

There have been attempts to build a wearable hydration sensor but no one has made the technology work reliably yet. It's a big potential market if someone can find a solution.

https://www.dcrainmaker.com/2016/09/bsx-announces-kickstarte...