A blood test detects early Alzheimer's as accurately as neuroimaging techniques or cerebrospinal fluid analyses, according to international research that is presented this week in the journal JAMA Neurology.
The new test, already commercialized, will represent "a before and an after in the way of diagnosing Alzheimer's", says Alberto Lleó, neurologist at Sant Pau hospital in Barcelona and co-author of the research.
Having a blood diagnostic test for Alzheimer's will help identify patients who can benefit from new treatments that slow the progression of the disease. It is expected that the European Agency of (EMA) will approve this year two of these treatments, lecanemab and the.
The blood test will also make it possible to evaluate the patients' response to the treatments. This, in turn, can facilitate the development of better therapies in the future, as it will be easier to study the effectiveness of drugs.
Alzheimer's diagnosis is currently based on two techniques that have limited use. On the one hand, a PET (positron emission tomography) neuroimaging technique that detects anatomical changes in the brain and which is too expensive to offer to all people suspected of having Alzheimer's. On the other, an analysis of the cerebrospinal fluid inside the spinal column, to which abnormal proteins from the brain reach, and which is also not offered to all patients because it is an invasive test.
To overcome these limitations, and to be able to offer a diagnostic test for Alzheimer's to more people, biomarkers of the disease have been sought in the blood. Of all those that have been studied in recent years, "the one that has proven to be the best candidate is the protein p-tau217", reports Alberto Lleó. It is a form of the tau protein that accumulates abnormally in the brains of people with Alzheimer's and is released into the blood.
The new research was based on comparing the analysis of the p-tau217 protein in blood with the analysis of cerebrospinal fluid and neuroimaging techniques. Unlike previous studies on the p-tau217 protein, this time a test from the ALZpath company that is already on the market has been used. This paves the way for its use in clinical practice, and not only in research contexts, reports Daniel, a neurologist at the memory unit at the Sant Pau hospital and also co-author of the research.
Data from 786 Alzheimer's patients from Spain, Canada and the United States were analysed. Two-thirds of the patients had been diagnosed before having cognitive impairment. They had an average age of 63 years and 64% were women. The 185 Spanish patients were part of the Sant Pau Neurodegeneration Initiative project, started in 2009.
In the three patient cohorts analysed, the reliability of the p-tau217 test in blood has been equivalent to that of diagnosis with neuroimaging and that of cerebrospinal fluid analyses. Researchers have shown that the protein is already in the blood from the preclinical phase of Alzheimer's, before the appearance of the first symptoms. Then its level increases as the disease progresses, correlative to brain atrophy and the level of abnormal proteins in the cerebrospinal fluid.
The increase in p-tau217 in the blood is consistent with the increase in beta-amyloid protein in the cerebrospinal fluid. Therefore, the blood test not only reports on the increase in tau protein in the brain but also on beta-amyloid. Tau and beta-amyloid are the two main proteins that are altered in people with Alzheimer's.
The test detects 95% of Alzheimer's cases, although there are about 20% of cases in which it is appropriate to confirm the result with a neuroimaging or cerebrospinal fluid test because the test results are not clear enough , reports Daniel Alcolea. Therefore, adds the neurologist, the most expensive or invasive techniques could be avoided in 80% of those affected.
"There is no longer any doubt that this test works; we finally have a diagnostic test for alzheimer's in blood", declares Alberto Lleó. "Now we need to implement it so that it reaches the patients".
"Biomarkers in blood are destined to revolutionize clinical care", conclude the authors of the research, which has been coordinated from the University of Gothenburg (Sweden), in JAMA Neurology. "These results highlight the importance of p-tau217 as an initial screening tool for cognitive impairment."
At first, the test will be useful in people who already have symptoms of Alzheimer's and in which establishing the diagnosis will allow decisions to be made about their treatment, informs Lleó. In particular, it will help decide which patients are candidates to receive the new antibodies against the beta-amyloid protein that slow the progression of the disease.
In people who do not have symptoms, the test will only be used for now in research contexts. There is still no approved treatment for the preclinical phase of Alzheimer's, so it is not considered justified to diagnose the disease at a time when it is not known how to act against it.
