Alzheimer's disease is a degenerative brain disorder that accounts for two-thirds of dementia cases. New treatments have been launched in quick succession recently, giving patients hope, but it is too soon to be reassured. All of the drugs work for patients in the early stage, yet there is still no adequate way to diagnose early. Existing tests require costly medical imaging or extraction of cerebrospinal fluid, causing major discomfort to patients and making them hard to perform easily.
A path has opened to conduct an Alzheimer's dementia test with a simple blood draw at neighborhood clinics. The U.S. Food and Drug Administration (FDA) said on the 13th (local time) that it had authorized Elecsys pTau181, a blood test co-developed by Swiss pharmaceutical company Roche and U.S. company Eli Lilly, as a diagnostic test for Alzheimer's disease that can be used in primary care settings.
Roche said in a press release that day that, in a clinical trial involving 312 people, the test could rule out Alzheimer's disease with 97.9% accuracy. This is not the first time that an Alzheimer's blood diagnostic test has received FDA authorization. In May, Japanese biotech Fujirebio also won FDA authorization for an Alzheimer's blood test. Does this mean the era of dementia blood tests is opening?
◇Finding Alzheimer's-causing proteins in blood
All of the blood tests approved by the FDA this year diagnose Alzheimer's disease by detecting specific proteins in blood. Alzheimer's disease is known to occur when amyloid beta and tau proteins abnormally accumulate in the brain.
Amyloid beta is originally a protein that protects nerve cells, but when it detaches from cells and forms clumps, it instead causes damage. Tau is also a protein that serves as a joint to maintain the structure of nerve cells, but when phosphate groups attach inside nerve cells and alter it, the protein becomes tangled clumps and causes problems with cognitive function.
Roche's Elecsys measures pTau181, a phosphorylated (p) form of tau protein, in plasma, the liquid component of blood. The test quantifies how much tau protein has been altered due to Alzheimer's disease. That does not mean Roche can immediately pick out Alzheimer's patients. Simply put, it diagnoses that a person with cognitive decline does not yet have Alzheimer's disease.
There are two kinds of diagnostic accuracy. Sensitivity is how accurately a test identifies people with the disease as having it, and specificity is how accurately it identifies people without the disease as not having it. By that measure, Roche's Elecsys diagnoses Alzheimer's disease with about 98% specificity.
Fujirebio's Lumipulse test measures the ratio of pTau217, a phosphorylated tau protein in blood, to amyloid beta 1-42. In theory, amyloid beta protein accumulates first in the brains of Alzheimer's patients, followed by aggregates of pTau181 and pTau217.
Lumipulse can diagnose both positive and negative for Alzheimer's disease. In a clinical trial of 499 people, 97% of those who were judged not to have Alzheimer's by Lumipulse were later confirmed negative in follow-up diagnostics. Among those who tested positive, 92% had the same result in follow-up tests. In other words, Lumipulse's diagnostic accuracy for Alzheimer's is a sensitivity of 92% and a specificity of 97%.
◇Likely to find patients in the gray zone of diagnosis
The medical community expects the two blood tests to greatly help in the early diagnosis of Alzheimer's patients who have been in the gray zone of diagnosis and thus undetected until now. Elecsys was authorized in the United States for adults aged 55 and older who show signs or symptoms of cognitive decline. The medical community estimates that in the United States more than 2 out of 5 people (42%) aged 55 and older have dementia. However, 92% of adults with mild cognitive impairment, the preceding stage, may go undiagnosed. Yet there is no simple testing method, so patients are not receiving appropriate treatment.
Joanne Pike, president of the Alzheimer's Association, said in a press release on the 13th, "This authorization is another important advancement toward expanding access to Alzheimer's diagnosis," and "By using a tool to exclude Alzheimer's disease in primary care settings, we can help identify the causes of cognitive decline more quickly."
Currently, Alzheimer's diagnosis involves scanning the brain with expensive positron emission tomography (PET) equipment to find amyloid beta plaques or directly extracting cerebrospinal fluid for analysis. If blood tests can filter out people who do not have Alzheimer's disease, appropriate treatment can be provided without difficult and costly tests. And if a person is judged to have Alzheimer's by a blood test, the diagnosis can be confirmed with existing tests and appropriate treatment can be started early.
The FDA in 2023 authorized Leqembi, co-developed by U.S. company Biogen and Japan's Eisai, as a treatment for Alzheimer's disease. The following year, Eli Lilly's Kisunla was also developed as a treatment for Alzheimer's disease. Both are antibody therapies that remove amyloid beta plaques accumulated in the brain, and they target early-stage patients, making early diagnosis all the more important.
◇Possibility of reducing medical spending in less developed countries
Alzheimer's blood tests could lead to enormous savings in medical costs. According to the World Health Organization (WHO), as of 2021 there are 57 million dementia patients worldwide, and the number could triple by 2050. The economic loss from dementia stood at $1.3 trillion (1851.46 trillion won) as of 2019, and 60% of patients live in low- and middle-income countries, making the burden difficult to bear. If blood tests become routine, early diagnosis and treatment will be possible, reducing medical costs accordingly.
The scientific community expects that as Alzheimer's blood tests diversify, patient diagnosis and treatment will advance further.
Ashvini Keshavan, a neurologist and biomarker researcher at University College London (UCL), said to the international journal Nature on the 17th, "More corporations are developing blood tests that measure biomarkers of Alzheimer's disease," adding, "This means there is competition in the field, which is positive."
Richard Isaacson, who established an Alzheimer's prevention clinic in the United States, said in a CNN interview on the 14th, "I remain cautiously optimistic about the future of Alzheimer's blood testing technology," adding, "I'm convinced we're only in the top of the first inning of a nine-inning baseball game."
References
Roche (2025), https://diagnostics.roche.com/us/en/news-listing/2025/fda-cleared-ptau181-alzheimers-blood-test.html
Nature (2025), DOI: https://doi.org/10.1038/d41586-025-03394-w