TL;DR
Alzheimer's starts quietly, with sticky plaques building in the brain long before memory slips, and a simple blood draw may now be able to spot them in people who feel perfectly fine. Blood tests for a protein called p-tau217, approved in the U.S. in September only for people who already have symptoms, are being lined up to find healthy volunteers for prevention trials, NPR reported. That matters because the only version of beating Alzheimer's that arrives in time is stopping it before the damage, and those trials need a cheap, fast way to find the right people and to see whether a treatment is working. The honest catch: nothing is approved yet for a healthy person who tests positive, so for now the realistic payoff of a positive result is a place in a trial.
Below the line, for paid subscribers: The full story: where it stands, how we got here and what's dated next; our Odds board on 4 milestones, starting with "A p-tau217 blood test is cleared to screen people without symptoms"; our labeled speculation on what it adds up to; and every source.