Experimental Test Checks for Signs of Plaque in Brain
By Charlene Laino
WebMD Health News
Reviewed by Laura J. Martin, MD
July 21, 2011 (Paris) -- Australian researchers report they're a step closer to developing a simple blood test for the early detection of Alzheimer's disease.
In early testing, the experimental screening tool proved about 85% accurate at determining the amount of Alzheimer's-associated plaque in people's brains.
If the findings can be replicated in large numbers of people, "they may lead to an economical screen that indicates whether a person is in the early stages of, or at risk of developing, Alzheimer's," says researcher Samantha Burnham, PhD, of the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Perth, Australia.
The test may also help doctors decide whether patients with memory loss need more expensive imaging scans to check for the disease, she tells WebMD.
About 5.4 million Americans have Alzheimer's disease, the most common form of dementia.
Current belief holds that amyloid plaque starts to build up in the brain seven to 10 years prior to the decline in cognitive skills that is often the first symptom of Alzheimer's, says Mary Sano, PhD, director of Alzheimer's disease research at Mt. Sinai School of Medicine in New York City.
Imaging scans using positron emission tomography (PET) and magnetic resonance imaging (MRI) can detect plaque and other brain changes indicative of Alzheimer's years before memory and other symptoms of the disorder are evident. But they are costly and impractical for use on a population-wide basis.
Amyloid levels can also be measured in the cerebral spinal fluid, and there "are a lot of data" indicating this approach can accurately predict which patients with mild cognitive impairment will progress to Alzheimer's, Sano tells WebMD. But a spinal tap is "quite an invasive procedure" that most people would prefer to avoid, she notes.
The new blood test, which spots nine proteins whose levels appear to correlate with amyloid levels in the brain, is one of hundreds in development.
What makes this one stand out is that it was validated against PET scans of the brain -- the gold standard -- in a relatively large study, says the Alzheimer's Association's Heather Snyder, PhD.
Still, further validation is needed, and the test needs to be standardized so it offers consistent results from one lab to another, she tells WebMD.
The findings were presented here at the Alzheimer's Association International Conference.
Blood Test for Plaque
To develop the noninvasive blood test, Burnham and colleagues used blood samples from 273 people participating in a large-scale study looking for new biomarkers for dementia.
First, they identified nine proteins that correlated with the amount of amyloid deposited in the brain.
"We set a cutoff level. Anyone above that point is thought to go on to get Alzheimer's disease in the next eight to 10 years. Anyone below that [level] is safe," she says.
When the blood test was administered to the same 273 participants, it correctly identified 83% of people with abnormally high levels of amyloid, as confirmed by PET scans. It also correctly identified 85% of people who didn't have high levels.
"That's pretty accurate when you consider that brain scans are only about 90% accurate," Burnham says.
The test was validated in 74 people participating in a U.S. study looking for Alzheimer's disease biomarkers.
Burnham doesn't know how much the new test will eventually cost, but points out that blood tests are typically inexpensive. She adds that CSIRO, which has a patent on the test, has approached several companies about commercial development.
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.