The first blood test to support early diagnosis of Alzheimer’s disease is now available outside of research settings in Australia – with another in the pipeline – and one in four GPs have had at least one patient ask about such tests in the last two weeks, according to a Healthed survey with 870 GP respondents so far.

While patients are already inquiring about these new blood tests, our survey suggests most GPs feel inadequately prepared to answer such questions.

When it comes to ordering Alzheimer’s specific blood tests, only 9% of GPs feel “very confident.” Ditto for their confidence in counselling patients about the results, implications and next steps following these tests – again just 9% of GPs said they feel very confident. And 40% said they’re “not at all confident” about ordering these tests.

Given that Roche’s pTau 181 plasma test was just TGA approved and listed on the Australian Register of Therapeutic Goods (ARTG) in October – and other Alzheimer’s blood tests that are still in development have also been in the news, it’s not surprising that people are a bit confused.

Here’s what you need to know.

What is the test that has just been approved?

Roche’s Elecsys® pTau 181 plasma test is known as a “rule out” test. It aims to support assessment of Alzheimer’s disease in the early stages (when newly approved monoclonal antibodies lecanemab and donanemab are most effective at slowing disease progression).

The test can “help rule out amyloid pathology in adults aged 55 – 80 years with subjective cognitive impairment/decline or suspected mild cognitive impairment (MCI) and who are being evaluated for Alzheimer’s disease and other causes of cognitive decline in primary, secondary or tertiary care settings,” a spokesperson for Roche explained.

The test was validated in a multicentre trial with 787 participants in Europe, USA and Australia, using amyloid PET as the reference method.

Understanding what the results mean

It’s crucial that patients – and doctors— understand that while a negative result on the test can help rule out Alzheimer’s does, a positive result does not mean someone has the disease.

The overall negative predictive value is high at 93.8%, but the overall positive predictive value is just 46.6%.

The predictive value also varies between healthcare settings. Because the prevalence of Alzheimer’s disease is greater in secondary or tertiary healthcare settings, the positive predictive value is higher than in primary care. For example, an analysis of the pivotal trial data estimated that the positive predictive value would be around 54% in a secondary real-world setting compared with around 33% in primary care.

While a negative result means there’s a low likelihood of amyloid pathology, those with a positive result should be referred to a specialist or memory clinic for confirmation of amyloid pathology via cerebrospinal fluid (CSF) or amyloid PET.

It’s also important to stress that the test only looks at Alzheimer’s disease pathology, and while this is common, it’s not the only cause of cognitive complaints and dementia, notes Dr Stephanie Daly, a GP and founder of Sensus Cognition who also works as a GP educator with Dementia Training Australia.

So the test could rule out Alzheimer’s disease, but the person may have vascular dementia, dementia with Lewy bodies, frontotemporal dementia – or something else such as anxiety and depression, she explains.

“So even if the result is negative, it would be important to continue to review the clinical picture,” Dr Daly adds.

How to access the test

The test is available now via the Florey Institute’s National Dementia Diagnostics Laboratory (NDDL), at a cost of around $200 per test.

At this stage, the pTau 181 plasma tests will be run once a week at the Florey Institute, with results expected to take one to two weeks for doctors to receive, but “if demand is high, the tests will be run more frequently,” according to Dr Qiao Xin Li of NDDL.

Doctors can request the plasma pTau 181 test on any pathology provider request form, Roche’s spokesperson said, adding that they are “hoping to establish additional testing sites around Australia in the near future.”

More blood tests are coming

This is just the first blood test to support early diagnosis and treatment of Alzheimer’s to become available in clinical settings.

Another blood test (Elecsys® pTau 217 plasma test) with stronger predictive value is in development, expected in the second half of 2026 “pending inclusion on the ARTG,” according to Roche.

Plasma phosphorylated-tau 217 (pTau 217) is considered “the most promising biomarker for reliable detection of Alzheimer’s disease pathology,” and is more accurate than the plasma pTau 181 test. Several companies are developing assays of this.

A study published in Alzheimer’s and Dementia last month found that combining two blood tests – the Lumipulse plasma pTau217 test and the Aβ42/40 ratio test – achieved over 93% accuracy and greater than 90% sensitivity and specificity.

Putting it into perspective

Professor Michael Woodward, geriatrician and head of Dementia Research and a senior clinician at the Memory Clinic at Austin Health, emphasises that the pTau 181 plasma test available now does a good job at ruling out the presence of amyloid – a biomarker of Alzheimer’s disease. However, while a positive result indicates a higher likelihood of amyloid, “you need a confirmatory test.”

“But the other test coming next year, the phosphorylated tau 217, that both rules out and rules in,” Professor Woodward says.

“In other words, if it’s negative, you probably don’t have Alzheimer’s. If it’s positive, you probably do have amyloid.  So that’ll be the test, because that’ll be helpful at both ends of the spectrum, whereas this is only really helpful at the rule-out end,” he explains.

Neither test predicts dementia more broadly, he adds – noting the importance of understanding the limitations of the tests and communicating carefully with patients.

“So for your patient that expresses concerns about their memory, you can now order a p-tau 181 and if negative you can reassure them that they do not have Alzheimer’s- but you do need to consider other causes for their concerns, including depression/anxiety,” Professor Woodward says.

Those with a positive test will require further investigations and support, so “it is best to send them to a memory specialist or clinic for further evaluation,” – and if Alzheimer’s disease is confirmed they can be assessed for suitability for the new amyloid-removing monoclonal antibodies, he adds.

Are GPs ready?

Healthed’s survey shows that many GPs don’t feel confident about the tests — and in fact, 58% of GPs said their main concern was lack of education on how to use them.

Dr Marita Long, a GP, Honorary Medical Advisor to Dementia Australia and Clinical Associate Professor at Wicking Dementia Research and Education Centre is concerned that GPs may feel pressure to order the tests without adequate support or education.

“As with many emerging tests—particularly those associated with new treatments — GPs are often encouraged to adopt them quickly, sometimes without adequate preparation or support,” Dr Long says.

“General practice is uniquely complex; we manage patients across all life stages, systems, and conditions. While I strongly support and advocate for the timely diagnosis of dementia and recognise the importance of subtyping to guide care, we need clearer information and education to use these tests confidently and appropriately.”

“These tests are looking at whether a patient’s cognitive changes are due to Alzheimer’s disease or not — they are not diagnosing cognitive impairment or dementia. And this is where some of the confusion may come in.”

“GPs must understand the indications, performance, limitations, potential confounders and implications of these tests, and ensure informed consent is obtained and documented before ordering them.”

“With targeted education, practical guidance, and adequate system support, I’m confident GPs will be more able to integrate these advances responsibly into primary care — but this will take time and it feels a bit like the horse may have already bolted!”