https://www.sciencedaily.com/releases/2022/10/221012194009.htm
It's not a medical test but rather a protocol of looking for a certain set of health and cognitive signs/events over time for each patient.
Mostly this will help the scientific community that studies dementia because they can now maybe find clinical participants who are at the very beginning of the disease (pre-diagnosis). Currently they have to find people who are already well into the disease (post-diagnosis) which makes getting their feedback and interpreting outcomes much less reliable.