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 they aren'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. 

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," she said.