Changes in the brain linked to Alzheimer’s disease can begin years before memory and other cognitive symptoms appear. Blood-based biomarkers offer a less invasive way to detect some of these biological changes. These include phosphorylated tau (p-tau), such as p-tau217 and p-tau181, and amyloid-beta measures such as the Aβ42/Aβ40 ratio. However, these tests do not directly measure memory loss, brain-cell loss or the severity of cognitive impairment.

Tau is a protein found in nerve cells. In Alzheimer’s disease, abnormal tau is linked to the formation of neurofibrillary tangles. The build-up of amyloid-beta is another biological change associated with the disease.