A simple blood test diagnoses Alzheimer's with 94.5% accuracy

Doctors correctly diagnose Alzheimer's disease about 75.5% of the time using standard clinical evaluations. A simple blood test bumps that number to 94.5%.

The study, published in the Journal of Neurology, tracked 200 patients — all 50 or older — who showed up at neurology clinics in Spain with cognitive complaints. The test measures levels of p-tau217, a protein that clumps in the brains of Alzheimer's patients and shows up in their blood. Right now, catching Alzheimer's early often means brain scans or spinal taps — procedures that are costly, uncomfortable, and not available everywhere. A blood draw sidesteps all of that.

For roughly a quarter of participants, the blood test flipped the diagnosis entirely. It went both ways — people misdiagnosed with Alzheimer's learned they had a different condition, and people whose symptoms had been chalked up to aging got the correct Alzheimer's diagnosis.

The blood test held up at every stage of cognitive decline, from early memory complaints to late-stage dementia. If widely adopted, it could replace the invasive and expensive procedures that currently keep millions of people from getting an accurate diagnosis.

Previously:

• A lifetime of reading may delay Alzheimer's by six years
• Alzheimer's breakthrough: Cancer drug wakes up sleepy brain cells
• Caffeinated coffee may stave off dementia