In older adults with preclinical Alzheimer’s disease and elevated amyloid pathology, higher baseline levels of plasma phosphorylated tau 217 are associated with a 47% greater rate of future cognitive decline over several years, as measured by the Preclinical Alzheimer Cognitive Composite.

In the brain, abnormal tau proteins clump into tangles inside nerve cells, and as these tangles grow, they damage the connections between cells. This damage spreads through brain networks that control memory and thinking, causing those connections to stop working properly. The amount of a specific form of tau in the blood matches how many tangles are present in the brain, so higher blood levels mean more damage is already happening, which leads to faster loss of thinking skills.