New blood test shows promise for Alzheimer’s disease diagnosis

Dementia is Australia’s second leading cause of death.
 
Without a medical breakthrough, more than 1.1 million Australians are projected to be living with the disease by 2056.
 
Currently available testing is limited, taking up to three years on average for a patient to receive a diagnosis from first seeking medical attention. But a new blood test, developed in Sweden and showing great promise for accurate and early diagnosis, could change all that.
 
‘The blood test detects a form of phosphorylated tau [P-tau181], which is one of the major components you find in the brain of people with Alzheimer’s disease,’ University of Melbourne Professor Christopher Rowe and director of the Australian Dementia Network (ADNeT) told newsGP.
 
The finding is backed in a new study in The Lancet Neurology.
 
Tau protein in the brain is one of the hallmarks of the disease, along with the clumpy plaques caused by the protein amyloid β.
 
To date, detecting changes to these proteins in cerebrospinal fluid has only been possible through invasive lumbar punctures or PET scans, expensive tests with no Medicare rebate, leaving patients out of pocket.
 
The new test is conducted using Simoa (Single Molecule Array) – a technology already used in Australia – and is 10,000 times more sensitive than previous immunoassays, making it possible to pick up incredibly low concentrations of proteins in blood.
 
In the coming weeks, to further validate the test on Australian cohorts, researchers from the ADNeT and the Australian Imaging Biomarkers and Lifestyle (AIBL) Flagship Study of Ageing are sending 500 blood samples to Sweden from participants who have had amyloid and tau PET scans done.
 
The plan is to then introduce the test to several ADNeT-affiliated memory clinics in major cities around Australia to collect information on accuracy, and affect patient care to obtain approval for widespread use in the community.
 
‘Logically, I would say this should be available within two years,’ Professor Rowe said.
 
Patients in Australia are currently diagnosed based on assessments of memory and other cognitive function – a process that has been shown to be only 70% accurate compared to post-mortem diagnosis, according to Professor Rowe.
 
‘Post-mortem studies, lumbar punctures and the PET scans have shown that these proteins build up many years before the symptoms appear. In fact, it is thought amyloid β comes first, then tau and then the cognitive decline,’ Professor Rowe said.
 
‘The whole process goes over about 30 years before we get to the dementia stage of Alzheimer's disease.
 
‘I think this is going to be a widely accessible, relatively inexpensive blood test for Alzheimer’s disease and for even finding people who are developing Alzheimer’s disease before they show any symptoms.’
 
Dr Marita Long, a GP and clinical educator for Dementia Training Australia, told newsGP such a blood test would give GPs greater confidence to diagnose with more certainty.  
 
‘Dementia’s probably one of the biggest public health crises we’re facing given the ageing population. In general practice we know that more than 50% of people living with moderate to severe dementia remain undiagnosed and it’s a leading cause of death in women, which is a pretty alarming statistic,’ she said.
 
‘One of the biggest barriers for us as GPs to diagnose dementia, and this is from studies that we’ve done, is that there is a fear of getting it wrong – a lack of confidence, a lack of training and education, and a feeling that there’s nothing we can do; there’s no treatment, there’s no cure.
 
‘I think having a blood test like this … would be amazing.’
 
The prospect of diagnosing patients earlier offers the opportunity to trial the use of existing dementia medications at a younger age, and provides more time to prepare patients and carers for the long haul. 
 
‘We can actually look at doing whatever we can to modify risk factors, to slow down the progression, to educate people with dementia around the sort of care options they have, to get the carers on track to what sort of challenges they might face so they can prepare for that – instead of having a diagnosis when someone’s a fair way down the track with the disease and falling apart, which is often how people present to us at general practice,’ Dr Long said.
 
While Dr Dimity Pond, who has a special interest in dementia and aged care, agrees a blood test could be a great addition to GPs’ armamentarium, she remains cautious, raising concerns over the possible consequences of a false-positive result.
 
‘The worst possible scenario – and I’ve seen this happen – is that the person’s labeled as having Alzheimer’s disease, has the house sold out from under them by the family and ends up in residential aged care unnecessarily,’ she said.
 
‘That’s a disaster for them personally, but also incredibly expensive for the healthcare system.
 
‘As with almost any blood test, it would have to be interpreted in light of the whole clinical picture of the patient. So if that blood test was positive but the person was functioning perfectly okay and showing no signs of dementia or Alzheimer's disease, then you’d have to query it.’
 
According to Professor Rowe, the test is so far showing 90% accuracy.
 
‘Which is pretty good – no test is 100%,’ he said.
 
‘So there will be the occasional false positive, false negative. It may well be that if you get a positive result, you are advised to have a lumbar puncture or a PET scan for confirmation.’
 
With more than 20 years’ experience in dementia research and patient care, Professor Rowe sees the blood test as a major breakthrough.
 
‘There’s a lot happening [in this space],’ he said.
 
‘This blood test is coming along just at the same time that the pharmaceutical industry is approaching governments for registration of some drugs that appear to be disease modifying. So we’re expecting big things in the early diagnosis and treatment of Alzheimer’s disease over the next couple of years.’
 
In the meantime, Dr Long believes it is important GPs remember they are best placed to make a difference in their patients’ lives.
 
‘There is a test coming, but let’s not wait for that. Let’s still keep ourselves centered on upskilling and educating as many doctors as we can to start identifying, recognising and getting people diagnosed in a timely fashion,’ she said.
 
‘We know can make a difference for people with dementia here and now.’
 
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