Study details

For the study, researchers looked at 1,213 patients in Sweden who had clinical evaluations due to cognitive symptoms between February 2020 and January 2024. Of the patients, 23% had subjective cognitive decline, 44% had mild cognitive impairment, and 33% had dementia.

Researchers then evaluated a plasma sample from each patient using the p-tau217 test, which measures the levels of a specific blood peptide known to be a marker of neurological damage due to Alzheimer's disease. They then compared the results of the test to doctor diagnoses and full-accuracy spinal tap tests.

The researchers found that dementia specialists who used standard methods like cognitive testing were accurate with their diagnoses 73% of the time, while primary care doctors were accurate 61% of the time. By comparison, the blood test diagnosed Alzheimer's with 91% accuracy, the study found.

Discussion

According to Sebastian Palmqvist, an associate professor at Lund University in Sweden and coauthor on the study, primary care is "the first, and in many cases, the final point of entry for these patients. Looking at the future, I think this is where the blood test can have the largest impact."

"Now that we have treatments that work best when they're started early, it adds a sense of urgency to diagnosis that was never there before," said Suzanne Schindler, a coauthor of the study and a neuroscientist at Washington University in St. Louis.

Getting an appointment with a dementia specialist can take weeks, even months, Schindler added. "With these blood tests, we could potentially decrease the amount of time that it takes from when patients develop symptoms to when they're diagnosed."

In a JAMA Neurology editorial, Gil Rabinovici and Lawren VandeVrede, both from the University of California, San Francisco, said the study "marks a milestone in blood biomarker development, as a blood test for Alzheimer's disease moves from the research world to dementia specialists and now into the hands of primary care physicians."

According to Maria Carrillo, chief science officer at the Alzheimer's Association, once blood tests are confirmed to be more than 90% accurate and are more widely available, they could potentially redefine the diagnostic workup for Alzheimer's.

"While, at this time, doctors in primary and secondary care should use a combination of cognitive and blood or other biomarker testing to diagnose Alzheimer's, blood tests have the potential to increase the accuracy of early diagnoses and maximize the opportunity to access Alzheimer's treatments as early as possible for better outcomes," she said.

Experts noted that blood tests should only be one step in the screening process and should only be used for people with memory loss and other cognitive decline symptoms, rather than people who are cognitively healthy who want to predict whether they'll develop Alzheimer's.

"If you would detect Alzheimer's disease pathology in the person without cognitive impairment, there's no therapies to offer," said Oskar Hansson, a professor of clinical memory research at Lund University and senior author of the study.

The pathology of Alzheimer's can start developing around 20 years before any symptoms, and in some cases, dementia doesn't develop, or people die from other causes before it does. Given that, there is a "risk of anxiety and other reactions, psychological reactions, to such a test result," Hansson said.

Rebecca Edelmayer, senior director of scientific engagement at the Alzheimer's Association, said the Association has asked experts to update clinical practice guidelines on how to use blood tests and aims to release recommendations in early 2025. (Goldman, Axios, 7/29; Robertson, The Hill, 7/28; Belluck, New York Times, 7/28; Jeong, Washington Post, 7/29; George, MedPage Today, 7/28)

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