Blood Test for Alzheimer’s up to 94% Accurate

New tests can detect dementia years before any outward signs appear.

Early brain changes due to Alzheimer’s disease may soon be detected with a simple blood draw in your doctor’s office, according to researchers. Doctors have been hoping for such a test for years — one that providers can administer in the office at a reasonable cost. They have been searching for an alternative to the $4,000 PET brain scan currently in use.

Dr. Richard Hodes, director of the National Institute on Aging, said that currently, the best use for the tests was in research because analysts can select and monitor people in much larger numbers than was possible previously for federally funded studies.

“In the past year, we’ve seen a dramatic acceleration in progress” on these tests, he said. “This has happened at a pace that is far faster than any of us would have expected.”

Research Specifics
The latest research, published in Neurology, uses mass spectrometry to measure two forms of amyloid protein in the blood: amyloid-beta 42 and amyloid-beta 40. All but 10 of the 158 study participants were cognitively normal, and each provided a PET brain scan used to detect Alzheimer’s. Scientists designated the blood sample and PET scan amyloid positive or negative, and the scan and bloodwork agreed 88% of the time. That was very good, but not accurate enough for clinical diagnosis.

Researchers decided to incorporate several known risk factors for Alzheimer’s. The risk of developing the disease doubles every five years after age 65, making age the biggest factor. Some people carry a genetic variant dubbed APOE4, raising their risk three- to fivefold. And sex is a factor, since two out of three patients are women.

When all of these factors were accounted for in the analysis, the accuracy of the blood test raised to 94%, with age and genetic status accounting for all of the improvement.

Another factor in the improved percentage was that scientists had initially labeled some blood results as false positives when the PET scan didn’t detect any disease. However, some of these people tested positive on subsequent scans taken an average of four years later. Far from being wrong, the blood test had been able to identify those with Alzheimer’s that the esteemed brain scan had missed.

Clumps of damaging amyloid-beta protein begin to form in the brain up to two decades before outward signs of the disease appear. Scientists can detect the level of the protein in the blood and use that information to predict if it is accumulating in the brain.

A handful of research groups around the globe have recently reported similar success. Though the techniques vary slightly, all of the groups are reporting high accuracy and earlier diagnosis.

“Everyone’s finding the same thing … the results are remarkably similar across countries, across techniques,” said Dr. Randall Bateman of Washington University School of Medicine in St. Louis, whose work is supported by the U.S. government and the Alzheimer’s Association. He guesses a screening test could be ready as soon as three years from now.

Source: Society of Certified Senior Advisors blog: Friday, November 29, 2019