A blood test detects Alzheimer’s early with as much precision as neuroimaging techniques or cerebrospinal fluid analysis, according to international research presented this week in the journal JAMA Neurology.
The new test, already marketed, will represent “a before and after in the way of diagnosing Alzheimer’s,” declares Alberto Lleó, neurologist at the Sant Pau hospital in Barcelona and co-author of the research.
Having an Alzheimer’s blood diagnostic test will help identify patients who can benefit from new treatments that slow the progression of the disease. The European Medicines Agency (EMA) is expected to approve two of these treatments, lecanemab and donanemab, this year.
The blood test will also allow us to evaluate the patients’ response to the treatments. This in turn may facilitate the development of better therapies in the future, as it will be easier to study the effectiveness of drugs.
The diagnosis of Alzheimer’s is currently based on two techniques that have limited use. On the one hand, a PET neuroimaging technique that detects anatomical changes in the brain and that is too expensive to be offered to all people suspected of having Alzheimer’s. On the other hand, an analysis of the cerebrospinal fluid found inside the spinal column, to which abnormal proteins from the brain reach, and which is not offered to all patients because it is an invasive test.
To overcome these limitations, and to be able to offer an Alzheimer’s diagnostic test to more people, biomarkers of the disease in the blood have been sought. Of all those that have been studied, “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 neuroimaging and cerebrospinal fluid analysis techniques. Unlike previous studies on the p-tau217 protein, on this occasion a test from the ALZpath company that is already on the market has been used, which opens the way to its use in clinical practice, and not only in contexts of research, reports Daniel Alcolea, neurologist at the memory unit of the Sant Pau hospital and also co-author of the research.
Data from 786 Alzheimer’s patients from Spain, Canada and the United States have been analyzed. Two-thirds of the patients had been previously diagnosed with 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 analyzed, the reliability of the p-tau217 blood test has been equivalent to that of diagnosis with neuroimaging or cerebrospinal fluid analysis. The protein is already found in the blood from the preclinical phase of Alzheimer’s, before the first symptoms appear. And then its level increases as the disease progresses, correlative to brain atrophy and the level of abnormal proteins in the cerebrospinal fluid.
The test detects 95% of Alzheimer’s cases, although there are around 20% of cases in which it is advisable to confirm the result with a neuroimaging or cerebrospinal fluid test because the test results are not clear enough. Therefore, reports Daniel Alcolea, 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 the blood,” declares Alberto Lleó. “Now we need to implement it so that it reaches patients.”
“Blood biomarkers are destined to revolutionize clinical care,” the authors of the research, which was coordinated from the University of Gothenburg (Sweden), conclude in JAMA Neurology. “These results highlight the importance of p-tau217 as an initial screening tool for cognitive decline.”
Initially, the test will be useful in people who already have symptoms of Alzheimer’s and in whom establishing the diagnosis will allow treatment decisions to be made, reports 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 in research contexts for now. There is still no approved treatment for the preclinical phase of Alzheimer’s and it is not considered justified to diagnose the disease at a time when it is not known how to act against it.
