Alzheimer's Blood Test: Levels Vary by Group, Signal Holds

Jeff's Daily Pick. A blood test is replacing brain scans to spot early Alzheimer's. In 15,612 people on four continents, its levels differed by background, but it tracked brain amyloid the same way.

In the United States, researchers at the Keck School of Medicine of USC analyzed screening data from the AHEAD 3 45 trials, which test lecanemab in people with brain amyloid but no symptoms. The study, published on October 12, 2026 in JAMA Neurology, asked whether a leading Alzheimer's blood marker behaves the same way across racial and ethnic groups. The marker, %p-tau217, is the share of tau protein phosphorylated at position 217 in plasma.

Who was studied

The analysis included 15,612 cognitively unimpaired adults aged 55 to 80, screened from July 2020 to October 2024 at 106 sites in Asia, Australia, Europe and North America. Mean age was 68.4, 63.7% were women and 36.9% carried the APOE e4 gene variant. Blood was measured before medical and cognitive exclusions, and eligible people went on to PET scans of brain amyloid.

What differed and what held

Levels of %p-tau217 were lower in Asian and Black participants than in White participants, and lower in Hispanic than in non Hispanic participants. APOE e4 carriers had higher levels across all groups, and the size of that APOE effect differed by race. The key clinical question is whether the marker still tracks amyloid. Higher %p-tau217 was consistently associated with more amyloid on PET, and that association showed no significant pairwise differences across racial groups. It did differ by ethnicity, as did the link with the PACC5 cognitive score.

The practical implication concerns thresholds. A blood test used to decide who gets a PET scan or enters a prevention trial uses a cut off, and if baseline levels run lower in some groups, a single cut off could under refer them. Earlier p-tau217 research drew mostly on White participants, which makes a dataset this diverse useful for calibrating those thresholds. Our piece on deep sleep and tau explains the tau side of Alzheimer biology.