Blood tests to screen for Alzheimer's disease on the horizon

To diagnose and treat Alzheimer's disease effectively, doctors say they need affordable and accessible tests to screen people at midlife and then stave off symptoms. Here's where researchers are at for the first step.

About 750,000 Canadians live with Alzheimer's disease or another form of dementia. Alzheimer's is the most common form, with symptoms such as memory loss, changes in judgment and mood or problems with language that are irreversible and eventually fatal.

Families and their physicians have long sought a blood test to accurately predict the development of Alzheimer's in people with memory problems in the hopes that early diagnosis and existing treatments could at least slow worsening symptoms.

Alzheimer's is thought to start when a sticky, misfit protein called beta-amyloid leads to brain-clogging plaques and tangles associated with killing off neurons.

The hope is to prevent amyloid from building up in the brain years before symptoms appear.

But so far, the only way to confirm that beta-amyloid has built up is with brain scans that are expensive and hard to get or spinal taps that are invasive and uncomfortable.

That's where blood screening tests could play a role.

In this week's online issue of the journal JAMA, Dr. Oskar Hansson, a professor of clinical memory research at Lund University in Sweden, and his team report that a combination of blood tests for specific forms of beta-amyloid and tau proteins correctly identified whether 1,213 Swedish participants, with an average age of 74 and memory problems, in fact had Alzheimer's about 90 per cent of the time.

"We see this as a major step towards global clinical implementation of an Alzheimer's blood test," Hansson said in a release from the Alzheimer's Association, which partly funded the research.

The experiment needs to be repeated to see how the test fares in more diverse populations, the researchers stressed.

In comparison, dementia specialists using standard methods not including PET scans or spinal taps were accurate 73 per cent of the time, and primary care doctors were correct 61 per cent of the time for the 500 participants who went to those general clinics, the researchers reported.

In the United States, labs have started selling a variety of tests to detect signs of Alzheimer's in blood, but theyaren't widely used since doctors have little to guide them on when to use the tests. None are formally approved for use by the U.S. Food and Drug Administration or by Health Canada.

High accuracy level needed

Dr. Suzanne Schindler, a neurologist at Washington University in St. Louis who was part of the Swedish study, said it can be difficult to tell whether Alzheimer's or something else is to blame for a patient's symptoms.

"I have patients not infrequently who I am convinced have Alzheimer's disease, and I do testing and it's negative," shesaid.

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Schindler, who helped lead a comparison of blood tests, said the Swedish one measures a form of tau that correlates with how much plaque buildup someone has. A high level signals a strong likelihood a person has Alzheimer's, while a low level suggests probably not. Tau is thought to reflect the spread of the disease in the brain.

Canadian geriatrician advises caution

Dr. Samir Sinha, director of geriatrics at Sinai Health and University Health Network in Toronto, said he's already receiving calls from patients asking if they should get the blood test. He's never ordered such a test andadvises caution at this point.

"Even if they did have a positive test, I could say you might have an increased risk, but I can't guarantee you will develop dementia," Sinha said.

It's important to do a test if you know what you're going to do with the result. This one doesn't necessarily give doctors and patients information they can actually act upon, he said.

Maria Carrillo, Alzheimer's Association chief science officer, said doctors and researchers should only use blood tests proven to have a greater than 90 per cent accuracy rate.

Future studies also need to evaluate how the blood tests could be more practical for hospital laboratory workers to conduct instead of outside labs, where the testscan cost more and require highly technical expertise.

It could be unethical to use the blood tests for people who don't have symptoms but worry about Alzheimer's in the familyexcept as part of research studies, given that there are currently no treatments to prevent the development of the disease.

What's more, Alzheimer's disease may not cause symptoms like memory problems for years. Standardpreventive steps include eating a healthy diet and getting enough exercise and sleep.

The findings were also presented on Sunday at the Alzheimer's Association International Conference in Philadelphia. Themaker of an injection used to help diagnose Alzheimer's disease also contributed funding.