Blood Test Can Identify Alzheimer’s Disease With 94% Accuracy Before Symptoms Even Appear

Researchers have discovered a blood test that can identify early markers of Alzheimer’s Disease with 94% accuracy.

The protein amyloid beta can build up in the brain two decades before symptoms of Alzheimer’s begin. By measuring levels of this protein present in the blood, researchers from Washington University School of Medicine in St. Louis could predict how much was building up in the brain.

When the team combined the blood test results with two other risk factors — age and the presence of the APOE4 genetic variant — the test was highly accurate.

Their findings bring us one step closer to identifying Alzheimer’s before symptoms appear, which can greatly impact clinical trials and future treatments.

Photo: Adobe Stock/Juan Gärtner

The research was published on August 1, 2019, in the journal Neurology. Researchers gathered 158 adults who were over 50 years old and gave each a PET brain scan and collected one blood sample within 18 months. Nearly every adult — 148 out of the 158 in the study — was cognitively normal at the time testing was done.

For the blood tests, researchers used a technique called mass spectrometry to find two specific forms of amyloid beta: amyloid beta 42 and amyloid beta 40. When levels of these two types decrease in the blood, that indicates that the amyloid beta deposits in the brain are going up.

Every single blood test and PET scan was classified as either amyloid positive or negative. Then researchers would compare the two and see if they matched.

To improve the accuracy of the blood test, researchers looked at other major risk factors for Alzheimer’s, including age (which is the largest known risk factor, as chances of developing Alzheimer’s double every five years after age 65), the genetic variant APOE4 (which increases the risk of developing the disease by three to five times), and gender (since two out of three Alzheimer’s patients are female). They found that sex did not significantly affect the accuracy, but the APOE4 gene and age did.

Photo: Adobe Stock/fizkes

For 88% of the time, the scan and the blood test agreed on whether the patient was positive or negative. However, when researchers added in data about age and APOE4 status, blood test results and pet scans matched 94% of the time.

For the patients who had a positive blood test but a negative amyloid PET scan, researchers found that this wasn’t a false positive. Rather, the patients were 15 times more likely over time to eventually get a PET scan positive for amyloid beta compared to those with a negative blood test.

This indicates that the blood test could be more accurate than a PET scan, which is currently the gold standard of detecting the disease.

Photo: Adobe Stock/Анна Ковальчук

A blood test for Alzheimer’s could be significant for multiple reasons. Currently, clinical trials for Alzheimer’s drugs are limited because it’s difficult to determine if someone has Alzheimer’s brain changes when they haven’t yet experienced any noticeable cognitive changes. A blood test could screen people for Alzheimer’s, speed up the efficiency and accuracy of clinical trials since medications could be tested out earlier in the process, and better find solutions for prevention.

Hopefully, a test like this will become available at doctors’ offices in the near future, and lead to possible treatments to slow or stop the disease.

Randall J. Bateman, MD, was the senior author of the study, and is the Charles F. and Joanne Knight Distinguished Professor of Neurology at Washington University School of Medicine in St. Louis.

“Right now we screen people for clinical trials with brain scans, which is time-consuming and expensive, and enrolling participants takes years,” said Bateman. “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.”

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