Before you test for familial Alzheimer’s disease blood biomarkers

A Youngtimers Guide ・ Last Reviewed Nov 12 2025

For those at risk of developing familial Alzheimer’s disease (FAD), blood biomarker testing offers a meaningful window into what is happening in the brain, sometimes decades before symptoms begin. That is a remarkable capability, and it comes with a responsibility to understand what the tests can and cannot tell us, to prepare emotionally, and to interpret results with the right support.

What is the actual blood test like?

Biomarker blood tests are not a special procedure. The experience of getting tested is no different from any routine blood draw. Roll up a sleeve, small poke, done.

After the blood draw, researchers spin the blood in a centrifuge to separate the blood into parts. Then, they analyze the plasma, which is the clear liquid portion of the blood after it has been separated.

How does one prepare for the results, emotionally?

These tests can reveal information about disease progression that arrives years, sometimes decades, before any outward symptoms. That is genuinely useful, but it can also be a lot to hold.

Before pursuing any of these tests, consider speaking with a genetic counselor or Alzheimer's specialist who understands FAD biology. A good counselor will help work through what the results might mean, how to interpret different outcomes, and how to make decisions that align with personal values and circumstances. Youngtimers has compiled information about finding a genetic counselor, which is something members of the community often do when they’re seeking out genetic testing.

If connecting with the right specialist feels like a barrier, the Youngtimers community can help. Our Peer-to-Peer Program can connect you with members of the Youngtimers community who have navigated the same decisions, or you can attend a Support Group.

Don’t look to Aβ42/40 ratio for insight into familial Alzheimer’s disease progression

The Aβ42/40 ratio, covered on our Key Biomarkers page, is one of the most widely ordered Alzheimer's blood tests. It is available through major labs, often included in standard panels, and commonly used as a screening tool for Alzheimer's. For most people being tested for sporadic, non-inherited Alzheimer's, it works reasonably well.

For FAD mutation carriers, the Aβ42/40 ratio is not a reliable basis for decisions about disease status or timing. P-tau217, NfL, and GFAP are far more informative for that purpose.

A well-meaning physician could order this test if they don’t know you carry an FAD mutation, or if they aren’t familiar with the specifics of why it doesn’t apply to FAD. Bringing a knowledgeable specialist into the conversation, ideally one familiar with FAD specifically, can help ensure the right tests are being ordered and that results are being interpreted in the right context.