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Human brains are destined to fail. Determining whether memory decline is a sign of more than typical aging requires technology that isn't always available, leaving specialists to rely solely on their experience and judgment to spot signs of dementia.
However, scientists have now confirmed that an already clinically available blood test can supplement current diagnostic methods where expensive scans and spinal fluid samples aren't options, and it appears to deliver extremely high accuracy as well.
Researchers at Lund University in Sweden led a team of scientists in evaluating whether a combination of protein ratios found in human serum can accurately detect Alzheimer's pathology in patients.
Some 55 million people around the globe live with dementia, mostly in the form of Alzheimer's disease.
While the processes at work involve a complicated mix of genetic and environmental factors, one thing all individuals with Alzheimer's have in common is a steady loss of key neurons associated with a marked rise in abnormal proteins.
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Those two proteins – beta-amyloid and tau – clump and tangle in ways that either directly damage cells or inflict a degree of assault by other immunological processes.
General practitioners and specialists often use CT scans that reveal this degradation of brain tissue in association with cognitive tests and self-reported symptoms to gauge whether a patient is likely to have Alzheimer's disease.
Yet even in a best-case scenario with a full range of diagnostic tools at their disposal, both primary and secondary care providers often fail to make the right call.
"Primary care doctors' accuracy in identifying Alzheimer's disease was 61 per cent, while specialist physicians were correct 73 per cent of the time," says Lund University neurologist Sebastian Palmqvist.
"This underscores the lack of good, cost-effective diagnostic tools, particularly in primary care, and indicates the potential improvement in diagnosis with the adoption of this blood test in healthcare settings."
Numerous studies conducted in recent years have highlighted the potential role of plasma protein measures in the diagnosis of Alzheimer's disease, specifically comparative ratios of the 'normal' and aberrant forms of beta-amyloid and tau.
While similar tests have been carried out on spinal fluid, a commercially available blood test would be far less invasive, less painful, and quicker to carry out in a regular clinic.
To confirm whether the blood test is as reliable, Palmqvist and his team recruited 1213 patients who were being evaluated for Alzheimer's by their family doctor or a specialist in Sweden some time between February 2020 and January 2024.
Around two-thirds of the patients had been classified as having either subjective cognitive decline or mild cognitive impairment, while the remaining third had already received a diagnosis of dementia based on a mix of clinical and cognitive tests.
In addition to the blood test, most patients also received a lumbar puncture for spinal fluid. The few who couldn't underwent a radionuclide-tagged PET scan instead to assess abnormal aggregations of proteins in the brain.
Comparing the results, both forms of assessment fared just as well, predicting Alzheimer's with a 90 percent accuracy.
The convenience of a blood test means more patients can receive an accurate diagnosis sooner, allowing them to receive the healthcare they require without delay.
"The test is already available in the USA and is likely to become available in many other countries soon," says senior researcher Oskar Hansson, a neurologist at Lund University.
"Initially, it will mainly be used in specialist memory clinics, and it may take approximately one to two years to implement guidelines and training in primary care."
This research was published in JAMA.
