There are new blood tests for Alzheimer’s. Should I have one?

Source: The Conversation (Au and NZ)

Australians have seen a flurry of headlines announcing the arrival of blood tests for Alzheimer’s disease.

The news follows the Therapeutic Goods Administration’s approval of new blood tests for clinical use and the launch of the Asia-Pacific Centre of Excellence for Alzheimer’s Disease Diagnosis at Neuroscience Research Australia (NeuRA) in Sydney.

These developments promise earlier, simpler and more accessible testing for Alzheimer’s, the most common form of dementia.

But what are these blood tests? What do they actually tell you? Should everyone over 60 ask their GP for one? And what happens if the result is positive?

What’s new?

Until recently, confirming Alzheimer’s usually required either specialised brain imaging (known as amyloid PET scans) or a lumbar puncture to examine proteins in the cerebrospinal fluid surrounding the brain and spinal cord.

Both approaches work well but have limitations. PET scans are not widely available and are expensive (although the Medical Benefits Schedule provides a subsidy). Lumbar punctures are invasive and patients are concerned they’ll be uncomfortable.

So researchers have spent the past decade or so asking whether the same biological changes seen in the brain could also be measured in blood.

The answer now appears to be yes.

Advances in laboratory technology mean tiny amounts of protein released from the brain can now be measured accurately in a standard blood sample.

This allows clinicians to estimate whether the biological changes associated with Alzheimer’s are likely to be present without immediately needing more invasive or expensive investigations.

There’s more than one Alzheimer’s blood test

There is no single blood test for Alzheimer’s. Rather, these tests look for biomarkers – biological signs that Alzheimer’s may be present in the brain. Several different blood biomarker tests are becoming available, each providing different information.

The test attracting the greatest attention detects a protein called phosphorylated tau 217 (pTau217). Studies show the presence of this abnormal form of the tau protein closely reflects the type of brain changes we see in Alzheimer’s. The test also performs remarkably well compared with PET brain imaging.

Another biomarker, pTau181, also detects an abnormal form of the tau protein. While useful, it is generally considered better at helping rule out Alzheimer’s brain changes than confirming them. So, increasingly, pTau217 is becoming the preferred biomarker because it provides greater diagnostic accuracy.

A third blood test looks for the APOE ε4 gene variant. This is not a diagnostic test at all. Instead, it identifies the strongest known inherited genetic risk factor for Alzheimer’s. Carrying the gene increases someone’s risk of Alzheimer’s, but it does not mean they will develop it.

What do these tests actually tell you?

These blood tests do not currently diagnose Alzheimer’s disease. They detect biological signs (biomarkers) indicating there may be brain changes associated with it.

Alzheimer’s remains a clinical diagnosis. That is, doctors will interpret blood biomarkers alongside a person’s symptoms, medical history, cognitive testing, neurological examination and, where necessary, brain imaging or cerebrospinal fluid analysis.

Many conditions can affect memory and thinking, such as depression, sleep disorders, thyroid disease, vitamin deficiencies, stroke and other neurological disorders.

So doctors will have to rule these out first. At this stage, a blood biomarker, such as the ones mentioned, cannot reliably do this for you.

Who are these tests for?

Another common misconception is that everyone should have one of these tests. Current evidence does not support this.

Instead, blood biomarker tests are most appropriate for people who already have persistent cognitive symptoms (such as memory loss), those with mild cognitive impairment, or people being assessed for possible Alzheimer’s.

At present, they are not recommended as routine screening tests for healthy adults without symptoms.

Brain changes associated with Alzheimer’s can develop many years before symptoms appear. Some people with abnormal biomarkers remain cognitively healthy for the rest of their lives, while others develop dementia much later.

Researchers are still learning how to interpret positive results in people without symptoms.

Why are these tests important?

Although blood biomarker tests are not perfect, they could substantially change the way Alzheimer’s is investigated.

In Australia, there are long delays in dementia diagnosis. Many people wait years between first noticing symptoms and having a diagnosis confirmed.

International estimates also suggest most people with Alzheimer’s are never formally diagnosed. The same may be happening in Australia.

Blood biomarker tests may speed up diagnosis.

Having an earlier diagnosis is also increasingly relevant as disease-modifying therapies emerge. Treatments such as lecanemab and donanemab can modestly slow cognitive decline in carefully selected people with early Alzheimer’s. However, these therapies are only appropriate for specific patients and require confirmation of underlying brain changes before treatment can begin.

What about cost?

These tests are not currently funded through Medicare. Patients are therefore likely to face out-of-pocket costs for testing, alongside specialist consultation fees and any additional investigations that may be still be needed.

The newly established centre of excellence aims to build the Australian evidence needed to support future Medicare funding and help develop national clinical guidelines for how these biomarkers should be used.

What should I ask my doctor?

If you are worried about changes in your memory or thinking, the first step is still to speak to your GP.

You can ask:

is Alzheimer’s one possible explanation for my symptoms?
would a blood test help clarify the diagnosis?
what would the result change?
would I still need additional testing?
what are the costs involved?

For now, Alzheimer’s blood biomarkers should be viewed as an important addition to clinical care rather than a replacement for it.

Combined with clinical assessment and emerging treatments, they have the potential to fundamentally reshape how Alzheimer’s is recognised and managed over the coming decade.

Joyce Siette does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Original source: https://analysis1.mil-osi.com/2026/08/04/there-are-new-blood-tests-for-alzheimers-should-i-have-one/