Accurate Blood Test for Alzheimer’s Disease

An accurate diagnosis of Alzheimer’s disease currently requires a sample of cerebrospinal fluid or a brain imaging test called a PET scan. Neither test can be done in primary care clinics, where most people with cognitive impairment are first seen.

These barriers slow or prevent the diagnosis of Alzheimer’s disease. The lack of an official diagnosis prevents people from receiving medications that could slow the progression of the disease. It can also prevent them from participating in studies of new treatments.

Researchers are working to develop simpler blood tests for Alzheimer’s disease. These tests measure Alzheimer’s-related proteins called beta-amyloid and tau. Abnormal buildup of certain forms of beta-amyloid and tau can cause them to leak into the bloodstream from the brain. Many blood tests for Alzheimer’s disease have shown promising results. However, to date, most studies of these tests have not been done in real-world settings such as community clinics.

In a new study, funded in part by the NIH, researchers led by Dr. Sebastian Palmqvist and Dr. Oskar Hansson of Lund University in Sweden collected blood samples from people being evaluated for cognitive symptoms. More than 500 older adults were recruited from local primary care clinics and nearly 700 from nearby memory care clinics.

The researchers used a test called PrecivityAD2. This test measures the ratio of two types of beta-amyloid as well as the proportion of tau made up of a specific type called p-tau217. Both of these measures have already been shown to predict a diagnosis of Alzheimer’s disease. In a previous study, the team had defined the levels of these molecules needed to confirm a diagnosis of Alzheimer’s disease.

In the new study, researchers compared the blood test results to those from a cerebrospinal fluid test or a positron emission tomography (PET) scan. They also compared the blood test’s performance to standard clinical assessments performed by doctors. These assessments include a physical exam, cognitive tests, and a CT scan of the brain. The results were published July 28, 2024, in JAMA.

In all participants, the blood test predicted an Alzheimer’s diagnosis with 88 to 92 percent accuracy. Further analysis revealed that measuring the proportion of p-tau217 alone produced similar results to those obtained with both measures.

The blood test performed significantly better than clinical assessments done without biomarker-based testing. These clinical assessments were 73% accurate in identifying Alzheimer’s disease when done in memory clinics, and only 61% accurate when done in primary care settings.

“We see this as a major step towards the global clinical implementation of a blood test for Alzheimer’s disease,” says Hansson. “Next steps include establishing clear guidelines on how a blood test for Alzheimer’s disease can be used in clinical practice, preferably by implementing these tests first in specialist care and then in primary care. This work is currently underway.”

Although the test used in the study is sold in the United States, it is not yet approved by the Food and Drug Administration (FDA) or covered by most health insurance plans. The study also needs to be replicated in more diverse populations than the one studied in Sweden.

—by Sharon Reynolds