WASHINGTON -- New blood tests could help doctors diagnose Alzheimer鈥檚 disease faster and more accurately, researchers reported Sunday 鈥� but some appear to work far better than others.
It鈥檚 tricky to tell if memory problems are caused by Alzheimer鈥檚. That requires confirming one of the disease鈥檚 hallmark signs 鈥� buildup of a sticky protein called beta-amyloid 鈥� with a hard-to-get brain scan or uncomfortable spinal tap. Many patients instead are diagnosed based on symptoms and cognitive exams.
Labs have begun offering a variety of tests that can detect certain signs of Alzheimer's in blood. Scientists are excited by their potential but the tests aren't widely used yet because there's little data to guide doctors about which kind to order and when. The U.S. Food and Drug Administration hasn't formally approved any of them and there's little insurance coverage.
鈥淲hat tests can we trust?鈥� asked Dr. Suzanne Schindler, a neurologist at Washington University in St. Louis who鈥檚 part of a research project examining that. While some are very accurate, 鈥渙ther tests are not much better than a flip of a coin.鈥�
Demand for earlier Alzheimer's diagnosis is increasing
More than 6 million people in the United States and millions more around the world have Alzheimer鈥檚, the most common form of dementia. Its telltale 鈥渂iomarkers鈥� are brain-clogging amyloid plaques and abnormal tau protein that leads to neuron-killing tangles.
New drugs, Leqembi and Kisunla, can modestly slow worsening symptoms by removing gunky amyloid from the brain. But they only work in the earliest stages of Alzheimer鈥檚 and proving patients qualify in time can be difficult. Measuring amyloid in spinal fluid is invasive. A special PET scan to spot plaques is costly and getting an appointment can take months.
Even specialists can struggle to tell if Alzheimer鈥檚 or something else is to blame for a patient鈥檚 symptoms.
鈥淚 have patients not infrequently who I am convinced have Alzheimer鈥檚 disease and I do testing and it鈥檚 negative,鈥� Schindler said.
New study suggests blood tests for Alzheimer鈥檚 can be simpler and faster
Blood tests so far have been used mostly in carefully controlled research settings. But a new study of about 1,200 patients in Sweden shows they also can work in the real-world bustle of doctors' offices 鈥� especially primary care doctors who see far more people with memory problems than specialists but have fewer tools to evaluate them.
In the study, patients who visited either a primary care doctor or a specialist for memory complaints got an initial diagnosis using traditional exams, gave blood for testing and were sent for a confirmatory spinal tap or brain scan.
Blood testing was far more accurate, Lund University researchers reported Sunday at the Alzheimer's Association International Conference in Philadelphia. The primary care doctors' initial diagnosis was 61% accurate and the specialists' 73 per centt 鈥� but the blood test was 91 per cent accurate, according to the findings, which also were published in the Journal of the American Medical Association.
Which blood tests for Alzheimer鈥檚 work best?
There鈥檚 almost 鈥渁 wild West鈥� in the variety being offered, said Dr. John Hsiao of the National Institute on Aging. They measure different biomarkers, in different ways.
Doctors and researchers should only use blood tests proven to have a greater than 90% accuracy rate, said Alzheimer鈥檚 Association chief science officer Maria Carrillo.
Today's tests most likely to meet that benchmark measure what鈥檚 called p-tau217, Carrillo and Hsiao agreed. Schindler helped lead an unusual direct comparison of several kinds of blood tests, funded by the Foundation for the National Institutes of Health, that came to the same conclusion.
That type of test measures a form of tau that correlates with how much plaque buildup someone has, Schindler explained. A high level signals a strong likelihood the person has Alzheimer鈥檚 while a low level indicates that鈥檚 probably not the cause of memory loss.
Several companies are developing p-tau217 tests including ALZpath Inc., Roche, Eli Lilly and C2N Diagnostics, which supplied the version used in the Swedish study.
Who should use blood tests for Alzheimer鈥檚?
Only doctors can order them from labs. The Alzheimer鈥檚 Association is working on guidelines and several companies plan to seek FDA approval, which would clarify proper use.
For now, Carrillo said doctors should use blood testing only in people with memory problems, after checking the accuracy of the type they order.
Especially for primary care physicians, 鈥渋t really has great potential to help them in sorting out who to give a reassuring message and who to send on to memory specialists,鈥� said Dr. Sebastian Palmqvist of Lund University, who led the Swedish study with Lund鈥檚 Dr. Oskar Hansson.
The tests aren't yet for people who don't have symptoms but worry about Alzheimer's in the family 鈥� unless it's part of enrollment in research studies, Schindler stressed.
That's partly because amyloid buildup can begin two decades before the first sign of memory problems, and so far there are no preventive steps other than basic advice to eat healthy, exercise and get enough sleep. But there are studies underway testing possible therapies for people at high risk of Alzheimer's, and some include blood testing.
The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute鈥檚 Science and Educational Media Group. The AP is solely responsible for all content.
