Neurology Central

A blood test for early Alzheimer’s disease demonstrates 94% accuracy in diagnosis

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A team of neuroscientists from the Washington University School of Medicine (MO, USA) have revealed that a blood test for Alzheimer’s disease may be moving closer to reality.

In the study, which has been published in Neurology, the researchers demonstrated that levels of amyloid-β (Aβ) in the blood can be measured and used to predict whether the protein has accumulated in the brain.

In addition to this, the investigators stated that when blood amyloid levels were combined with two major risk factors – age and the presence of the genetic variant APOE4 – that people with early Alzheimer’s brain changes could be identified with a 94% accuracy.

The test utilized mass spectrometry to precisely measure the amounts of Aβ42 and Aβ40. The ratio of the two forms is reported to go down as the amount of Aβ deposits in the brain goes up.

Within the study, 158 adults above the age of 50 were included and all but ten of the participants were cognitively normal. Each person provided at least one blood sample and underwent one PET brain scan. The samples and scans were then classified as amyloid positive or negative, and it was determined that the blood test from each individual agreed with their PET scan 88% of the time.

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To improve the accuracy of the test, the researchers incorporated several major risk factors for Alzheimer’s, including age, genetic variant (APOE4) and sex. When these risk factors were included in the analysis, the team identified that age and APOE4 status raised the accuracy of the blood test to 94%.

“Sex did affect the Aβ ratio, but not enough to change whether people were classified as amyloid positive or amyloid negative, so including it didn’t improve the accuracy of the analysis,” explained first author Suzanne Schindler (Washington University School of Medicine).

Further to this, the results of some people’s blood tests were initially considered to be false positives because their blood tests came back positive for Aβ, however, their brain scans came back negative. Some individuals with these mismatched results were subsequently tested 4 years later and their brain scan results came back positive. According to the researchers, these findings suggest that the initial blood tests had flagged early signs of the disease that were missed by the brain scan.

As part of the study, the team also analyzed the enrollment process for a prominent Alzheimer’s prevention trial (known as the A4 study), which used PET scans to confirm the presence of early Alzheimer’s brain changes in potential participants. The investigators determined that prescreening with a blood test followed by a PET scan for confirmation could have reduced the number of scans required by two-thirds.

Senior author of the study, Randall Bateman (Washington University School of Medicine), commented: “If you want to screen an asymptomatic population for a prevention trial, you would have to screen, say, 10,000 people just to get 1500 or 2000 that would qualify.”

“Reducing the number of PET scans could enable us to conduct twice as many clinical trials for the same amount of time and money… If we can run these trials faster, that will get us closer to ending this disease,” Bateman concluded.

Source: Schindler SE, Bollinger JG, Ovod V et al. High-precision plasma β-amyloid 42/40 predicts current and future brain amyloidosis. Neurology doi:10.1212/WNL.0000000000008081 (2019); https://medicine.wustl.edu/news/blood-test-is-94-accurate-at-identifying-early-alzheimers-disease/

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