A window into the brain

For many years, diagnosing conditions such as Alzheimer’s disease has relied largely on clinical judgment.

A patient (or their family) reports memory concerns. A doctor or specialist asks questions and performs cognitive testing, as well as blood tests, to rule out reversible causes of memory loss.

Brain scans have been available for a few decades but until relatively recently, in daily practice, we, as doctors, have been limited to using CT or MRI scans.

These look at the structure of the brain and can only hint at what disease process might be driving memory loss.

A lumbar puncture (spinal tap) has been a helpful and more definitive test available for some time, but is not widely accessible or appealing to the recipient.

We are now entering a new era, however, where we have more accessible and more sensitive and specific so-called biomarkers.

When it comes to the brain, this may involve functional brain scans or blood-based tests looking at the proteins found in Alzheimer’s disease. These tests may be abnormal many years before a person even shows symptoms of the disease. Firstly, a scan I find very helpful is an FDG-PET which measures glucose (sugar) uptake in the brain. In Alzheimer’s disease, certain regions become less active. This test can also detect other causes of cognitive impairment, including frontotemporal dementia and Lewy body disease.

In metropolitan areas of Australia at least, this is relatively easy to obtain, and is a test I frequently use alongside an MRI.

Also increasingly available is another type of PET scan, known as an amyloid PET. Rather than measuring sugar, this test detects the build-up of amyloid in the brain: a hallmark protein of Alzheimer’s disease.

The main barrier to this test is the cost. In Brisbane, you are looking at paying about $2500. Alongside a lumbar puncture, it is our most accurate way of detecting Alzheimer’s disease while a person is still alive.

This type of test has become particularly important with the advent of new treatments for Alzheimer’s disease: monoclonal antibodies that require a person to have a positive scan (or a positive lumbar puncture) before they can be used.

There is, however, an important point to make. The presence of amyloid does not necessarily mean a person has dementia.

Many older adults have amyloid in the brain and remain cognitively normal. This is a recurring theme in brain health.

Biology does not always translate neatly into symptoms.

With the expense and involved nature of these brain scans, it is unsurprising that there has been a push to develop blood tests that might help us detect Alzheimer’s disease, and these are now available in Australia.

The two main tests involve the detection of tau: the other Alzheimer’s protein. One of these tests, p-tau 181, was approved for use by the Therapeutic Goods Administration in late 2025 and has been heralded as a helpful screening tool for GPs. It costs about $300.

A negative p-tau 181 test result means it is highly unlikely that Alzheimer’s disease is present. This, of course, can be very reassuring, though it does not rule out other causes of dementia.

For now, these investigations are best used selectively, in the right clinical setting, and interpreted with care. They can clarify a diagnosis, guide treatment decisions and, in some cases, provide reassurance.

Their availability raises other important questions, however. When should we test? What should we do with the information? And, perhaps most importantly, does knowing earlier change outcomes?

As with many advances in medicine, the challenge is not just in developing the technology, but in using it wisely.

 Kailas Roberts is a psychogeriatrician and author of Mind Your Brain: The Essential Australian Guide to Dementia, available at bookstores and online. Visit yourbraininmind.com or uqp.com.au