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Blood Test Detects Early Stage Alzheimer's With 94 Percent Accuracy, Surpassing The Current Gold Standard


Alzheimer's on MRI. Shutterstock/Raksthaput

One big problem affecting Alzheimer's research today is that it is almost impossible to identify the disease in the earliest stages. So often, by the time it is detected, the debilitating symptoms are already present – and at that point, it may already be too late.

This could change with the development of a blood test scientists say can diagnose up to 94 percent of Alzheimer's cases 20 years before the disease really sets in. Researchers from the Washington University School of Medicine in St Louis described the test in the journal Neurology.


The test is based on levels of amyloid-beta in the blood, which predicts how much of the protein has collected in the brain. It is an upgrade of an earlier edition revealed two years ago that used mass spectrometry to measure ratios of amyloid-beta 42 and amyloid-beta 40. When the ratio has been determined, the results are compared to the patient's age and the presence (or lack) of the genetic variant APOE4 – aka two important risk factors for Alzheimer's.

The team recruited 158 adults (aged 50+), all but 10 of whom were described as being cognitively normal. Each patient produced at least one blood sample and underwent at least one PET scan, the method traditionally used to diagnose Alzheimer's. Each blood sample and PET scan was then labeled either amyloid positive or amyloid negative depending on the results it produced.

The researchers were looking for a match and they got it in 88 percent of cases. When they involved certain risk factors, the accuracy of the blood test jumped to 94 percent. 

Those risk factors included age (the chance of developing Alzheimer's doubles every five years) and APOE4 (presence of the genetic variant increases the chance of developing the disease three-to-fivefold). The team also tested gender (women outnumber male Alzheimer's patients 2 to 1), but that didn't seem to have much of an effect on the results.


Interestingly, the blood test results of some patients initially thought to be false positives were, in fact, true positives. The researchers had dismissed these results because they did not match the patient's (negative) PET scan. However, later brain scans confirmed they had been right all along. This suggests the blood test had flagged the disease at an earlier stage – and is more reliable than the current gold standard PET scan.

The team hopes such a test could be available at your local doctor's sometime soon. 

But there lies another problem. While earlier detection is a step in the positive direction, there still isn't a treatment that can really stop the disease progressing, or "cure" Alzheimer's. (Though there may be ways to relieve some of the symptoms.) The good news is that early detection like this can tackle a major obstacle to Alzheimer's research, which is that it is difficult to (quickly and cheaply) identify participants for clinical trials before they start to show symptoms.

There is a growing consensus among experts that to manage or treat Alzheimer's, it needs to be caught as early as possible – before symptoms start to show. By the time symptoms do show, the brain may be too damaged to fix.


"Right now we screen people for clinical trials with brain scans, which is time-consuming and expensive, and enrolling participants takes years," senior author Randall J. Bateman, MD, Professor of Neurology, said in a statement.

"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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