For decades, the earliest detectable sign of Alzheimer's disease was considered to be amyloid plaque accumulation on a brain PET scan — a change that typically appears 10 to 20 years before symptoms begin. But a study published April 14, 2026 in Nature Communications by investigators at Harvard-affiliated Mass General Brigham has moved that frontier even earlier: a blood test measuring a protein called plasma phosphorylated tau 217 (pTau217) can detect changes consistent with early Alzheimer's disease progression before amyloid PET scans show anything abnormal.
This is not a marginal technical improvement. It represents a fundamental shift in the timeline of Alzheimer's detection — and consequently in the window for intervention, clinical trial enrollment, and preventive strategies.
