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Blood Test Identifies Alzheimer’s Disease Before Symptoms Start

August 06, 2019

A test that measures levels of amyloid beta in the blood, when factored with a person’s age and the presence of the genetic variant APOE4, can identify brain changes from early Alzheimer’s disease with 94% accuracy, according to a study published online in Neurology.

The blood test appears to be even more sensitive than gold-standard positron emission tomography (PET) scans at detecting the start of amyloid beta accumulation in the brain.

The test uses mass spectrometry to measure the ratio of amyloid beta 42 and amyloid beta 40 in the blood. As amyloid beta deposits build up in the brain, the ratio in the blood goes down.

For the study, researchers took blood samples and PET brain scans of 158 people older than 50, all but 10 of whom were cognitively normal. Blood samples and PET scans were then classified as amyloid positive or negative.

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Initially, results from each participant’s blood test and PET scan agreed 88% of the time. When researchers incorporated age and APOE4 status into the mix, however, the accuracy rose to 94%. The risk of developing Alzheimer’s disease doubles every 5 years after age 65, researchers explained, while the genetic variant APOE4 increases the risk by 3 to 5 times.

In multiple cases in which a person’s blood test was positive for amyloid beta but the PET scan was negative, brain scans taken an average 4 years later tested positive. The finding suggests the initial blood tests had caught early signs of Alzheimer’s disease that brain scans did not.

While the test could be available for use in clinical practice in several years, researchers are especially excited about its application for clinical trials testing potential Alzheimer’s disease treatments.

“Right now, we screen people for clinical trials with brain scans, which is time-consuming and expensive, and enrolling participants takes years,” explained senior author Randall J. Bateman, MD, a neurology professor at the Washington University School of Medicine in St. Louis, Missouri.

“But with a blood test, we could potentially screen thousands of people a month. That means we can more efficiently enroll participants in clinical trials, which will help us find treatments faster, and could have an enormous impact on the cost of the disease as well as the human suffering that goes with it.”

—Jolynn Tumolo


Schindler SE, Bollinger JG, Ovod V, et al. High-precision plasma β-amyloid 42/40 predicts current and future brain amyloidosis. Neurology. 2019 August 1;[Epub ahead of print].

Bhandari T. Blood test is highly accurate at identifying Alzheimer’s before symptoms arise [press release]. St. Louis, Missouri: Washington University School of Medicine in St. Louis; August 1, 2019.

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