Alzheimer’s blood tests are advancing diagnosis. What can they really tell us?
New blood-based biomarkers for Alzheimer's disease, such as p-tau217, are improving the ability to detect biological signs of the disease before cognitive symptoms appear. However, experts caution that these tests indicate pathology rather than a definitive diagnosis of dementia or a timeline for decline.
Why it matters
These diagnostic tools represent a significant shift in neurology, allowing for earlier detection, though they require careful interpretation to avoid patient anxiety.
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.
Blood tests do not directly detect plaques or tangles in the brain. They measure proteins or changes in proteins in the blood that can reflect processes taking place in the brain.
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