A BLOOD TEST to diagnose Alzheimer’s disease has shown potential to detect chemicals in the blood that are specific for Alzheimer’s. This breakthrough could allow doctors to not only identify symptomatic patients with the disease, but also to identify people with no symptoms who are at risk of developing the disease, and thus begin interventions.
Over the last two decades, the medical field has made progress in detecting the disease by identifying specific diagnostic biomarkers, or biological signs of disease. Two key biomarkers, amyloid protein, found in plaques, and tau protein, found in tangles, became the targets outside of the brain tissue itself, since their presence in the brain defines the disease.
With the identification of these biomarkers, doctors could test patients to see if either amyloid or tau, or both, were abnormal in patients in whom they suspected Alzheimer’s. But the testing has not been easy or cheap.
One way was a spinal tap, whereby doctors could obtain cerebro-spinal fluid, the fluid around your brain and spine, and measure levels of tau and amyloid, which change if the disease is present.
Another method involves imaging the brain using a positron emission tomography (PET) scan following administration of compounds (amyloid or tau “tracers”) that bind one of the proteins that accumulates in the Alzheimer brain.
The impact of these advances is big, especially in research and clinical trials, where maximum likelihood of the right diagnosis is required. But the medical community urgently needs a more convenient, less expensive, less “invasive” way to diagnose Alzheimer’s.
Blood tests measuring amyloid and tau proteins have become much more sensitive and accurate enough to allow their possible future use as routine aids in Alzheimer’s disease diagnosis.
To be useful, the tests have to be nearly perfect predictors. Many aren’t there yet; so far, they seem to get it right up to over 85% of the time. And the accuracy will be very important if they’re to be used to screen people for positive tests and enter those people into clinical trials.
The newest blood assay for the tau protein, developed to look for a different site on the tau molecule than other tau tests, has now emerged with the highest accuracy yet – with data from three different large populations of patients.
In these studies, the sensitivity – or the ability to detect the disease when it is really there – and the specificity – negative test in people who do not have Alzheimer’s – were above 90% to 95%. It even detected elevated tau in the blood of people who had the disease in their brains but had not yet had any symptoms, identifying people at risk for the disease to enroll in trials to prevent the disease. These tests mark real progress. Cost-effective screening and diagnostic tests will help reach the goal of finding novel treatments that can better treat the clinical symptoms of Alzheimer’s or delay its development, or both. By Manny Palomar, PhD (EV Mail September 26-October 2, 2022 issue)