‘Breakthrough’ test for early dementia diagnosis a step closer

Further progress has been made in the development of a blood test to detect dementia, which has the potential to replace the current invasive and expensive options.
 
Recently published Swedish research used samples from around 800 people across three countries to determine how well the blood-based Alzheimer’s test, plasma pTau217, compared to the current available diagnostic tools of positron emission tomography (PET) scans and cerebrospinal fluid (CSF) tests from lumbar punctures.
 
The work, in collaboration with ALZPath, who developed the blood-based biomarker plasma pTau217 for early diagnosis of the disease, found that a commercially available blood test ‘accurately identified biological Alzheimer’s disease’.
 
The researchers found that blood and CSF tests performed exactly the same, with the blood test almost 95% accurate, which they say could eventually replace CSF.
 
While Australian experts say it shows much promise, approval for clinical use, as well as subsidised costs, are needed.
 
University of Melbourne Professor Chris Rowe is Director of the Australian Dementia Network (ADNeT). He told newsGP there is ‘lots to talk about’ on this subject.
 
‘Plasma pTau217 is a good test for Alzheimer’s disease,’ he said.
 
‘The Swedish paper that got so much press is the latest in a huge number of studies from across the world, including here in Melbourne, that have shown measuring pTau217 in blood is accurate for revealing the presence of Alzheimer’s disease in the brain even in the presymptomatic stage, but especially accurate when early symptoms have developed.’
 
But Professor Rowe said uncertainty remains as to when the test will become clinically available domestically.
 
‘The required equipment is available in several Australian cities and the kits to do the test can be purchased now but are specified as for research-use only,’ he said.
 
‘So we have a test, it works, it can be done now, but needs approval for clinical use by the Therapeutic Goods Administration or an ethics [committee], or an appropriately structured hospital committee for internal clinical use.
 
‘And it needs a Medicare rebate – [this is] the most significant impediment at present. The cost of the blood test will be between $200–350. Well-heeled patients will be able to have blood sent to the USA soon for testing but that will cost considerably more.’
 
In November 2021, Professor Rowe welcomed the addition of PET scans to the MBS to help cover the cost of the diagnostic tool for more accurate and early diagnoses.
 
But Alzheimer’s disease blood biomarkers have emerged as ‘scalable tools for clinical evaluation, trial recruitment, and disease monitoring’, the Swedish study authors state, and they show promise to ‘substantially reduce’ reliance on CSF or PET scans in specialised dementia care.
 
Dr Marita Long is a GP with a special interest in dementia. She told newsGP while it is exciting to see the test is getting closer to the primary care space, there is still ‘lots to iron out.’
 
‘Once all the finer details of the tests are sorted out it should be able to give us as GPs the confidence to deliver a more timely diagnosis of dementia, and ultimately mild cognitive impairment, due to Alzheimer’s disease,’ she said.
 
‘This will allow us to intervene to slow down the progression of the disease by modifying any risk factors, offering rehabilitation and as well as initiating any medical treatments.’
 
Currently, GPs have the option of using cholinesterase inhibitors and/or an NMDA receptor antagonist for dementia due to Alzheimer’s disease, Dr Long said, with these medications needing to be initiated in consultation with a non-GP specialist, such as a geriatrician, neurologist or old-age psychiatrist.
 
Should they become available for use in general practice, the blood tests should still be used alongside routine care, Dr Long highlights.
 
‘Blood biomarkers will be an adjunct and not replace the need for comprehensive history taking, examination and exploration of any reversible or contributing causes of cognitive decline in a patient,’ she said.

Dr Marita Long is anticipating use of the blood test in primary care, as it could have significant impacts on dementia diagnoses.
 
For now, the pTau217 test is available only for scientists to purchase for research studies, with doctors in the US soon able to order the test for use with patients. ALZPath has said as demand increases, large hospital and regional labs could start performing the test in the next few years.
 
In Australia, work is also well underway in this space, led by Professor Rowe.
 
‘ADNeT and the Australian Imaging, Biomarkers and Lifestyle Study of Ageing, working together with CSIRO, have several publications on pTau217 and several more currently under review confirming over 90% accuracy, compared to amyloid and tau PET scanning,’ he said.
 
ADNeT has also secured funding from the Department of Health and Aged Care to run a trial of the blood test in primary care to assess its impact on reducing delays in diagnosis of Alzheimer’s disease.
 
‘The latter is becoming important with the likely availability of anti-amyloid infusions later this year that slow disease progression and are much more beneficial if given early,’ Professor Rowe said.
 
In stage one of this project Professor Rowe and his team, including RACGP representatives, will be offering an online survey to assess knowledge among GPs on early detection and diagnosis of Alzheimer’s disease, then provide an educational video on the topic including discussion of the emerging blood tests and new anti-amyloid treatments expected to be available later this year.
 
‘We will then select about 50 GPs who express interest in further participation on the survey/video/follow-up survey … to assess the blood test and record management impact, impression of usefulness and earlier referral to memory specialists, ie hopefully with a lower degree of cognitive impairment than current practice,’ Professor Rowe said.
 
Should the test become universally available in Australia, Dr Long believes it could have profound benefits for the wider population.
 
‘With an ageing population we are going to be seeing more people who are living with dementia – a more timely diagnosis means we can intervene earlier and improve the lives of people living with dementia,’ she said.
 
‘We know that many people in the community remain undiagnosed so anything that can assist the process of an earlier diagnosis will have a significant impact on the health of the individual, the care partners and the health system.’
 
And with the advent of new treatments on the horizon, an earlier diagnosis will be ‘crucial’ to ensure eligible candidates for these treatments are identified as early as possible, according to Dr Long.
 
‘There has been some talk that these new medications can slow down the progress of the disease, potentially reverse, or even prevent the onset of symptoms,’ she said.
 
‘It’s early days but these drugs are the first breakthrough there has been since the late 1990s.’
 
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