Blood tests in familial Alzheimer's disease symptom onset

A Youngtimers Guide ・ Last Reviewed Mar 31 2026

Not long ago, the only way to confirm Alzheimer's disease was through an autopsy after death. Then came PET scans, specialized brain imaging that could detect the disease while someone was still alive. That was a revolution. But PET scans are expensive, hard to access, and require travel to specialized centers.

Today, we have something far more accessible: a simple blood draw can test for biomarkers that provide insight into what is happening inside a person’s brain.

These blood tests can now detect changes in the brain that begin more than 20 years before any memory symptoms appear.

This is only possible due to familial Alzheimer's disease (FAD) families themselves. For decades, volunteers with and without FAD genetic mutations agreed to regular testing, brain scans, and, ultimately, brain donation after death. Their sacrifice gave researchers the data needed to understand what these blood markers actually mean, and when they start to move.

These blood tests and biomarkers are exciting developments. For people who know they’re genetically at risk to develop FAD, the blood tests raise a lot of questions. It’s important to understand what you can learn, and then to consider what you actually want to learn.

This guide explains:

• What are blood biomarkers?

• Which biomarker tests are helpful, and which are not?

• What should a person know before they test?

• The typical phases of symptom onset in Familial Alzheimer’s disease

• How to use the information we can learn from blood tests and biomarkers