TL;DR
A blood test that spots the early biology of Alzheimer's has had a frustrating gap: it could say plaque was probably building in a healthy person's brain, but not how soon, or whether, thinking would start to slip. A new study begins to fill that in. Across 2,684 older adults who had no thinking problems, people whose blood carried very high levels of the marker had about a 4-in-10 chance of measurable decline within five years. It is not a diagnosis, and no drug is yet approved for people who test high. Our odds that a p-tau217 blood test is cleared to screen people without symptoms: 85%, likely by 2030. What it does give is the arithmetic that prevention trials need: a way to find the people most likely to decline soon, so a treatment that works could show it in a few years with a modest number of volunteers, instead of a decade with thousands. For a breakdown of the odds on screening healthy people and a timeline of the steps toward prevention, subscribe.
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