Study Finds That a Blood Test Can Accurately Detect Alzheimer’s Disease
An expert explains the promise of a blood test that was shown to make correct diagnoses about 90% of the time.
A study published recently in JAMA found that a blood test was highly accurate at diagnosing Alzheimer’s disease in individuals with memory loss. The blood test was also more accurate than providers who used only cognitive tests and imaging to come to a diagnosis.
Participants of the JAMA study included 1,213 patients with cognitive symptoms who were undergoing clinical evaluation in primary and secondary care. The blood test measured biomarkers, such as plasma phosphorylated tau 217 (p-tau217).
Results found that the blood test was accurate at diagnosing Alzheimer’s 90% of the time in patients with cognitive symptoms. Dementia specialists who used standard clinical evaluations, such as cognitive exams, but did not include PET scans or spinal taps, had a diagnostic accuracy of 73%, while primary care doctors who used the same approach were 61% accurate.
Dr. Lawrence S. Honig
“The blood test is one way of evaluating the same thing that spinal fluid and PET scans may see, which is determining the biological process going on in a patient who is experiencing Alzheimer’s disease symptoms, such as memory loss,” says Dr. Lawrence S. Honig, a neurologist at NewYork-Presbyterian/Columbia University Irving Medical Center.
While the study’s results were promising, Dr. Honig notes that the test would not be for people who may be concerned about Alzheimer’s and who are not experiencing symptoms. Additionally, the blood test is currently expected to be only one step in the diagnosis process, alongside other screening methods, such as gold-standards like PET scans and spinal taps.
Other than memory loss, signs and symptoms of Alzheimer’s include difficulty with reasoning and concentration, decreased judgment, difficulty completing routine tasks, and changes in personality and mood. But a key indicator of the disease is the accumulation of proteins in the brain, including beta-amyloid and tau. Tau forms later on after amyloid clumps have already developed and is also linked more closely to cognitive decline. “The blood test works by measuring these proteins in the blood,” explains Dr. Honig. “But it may not be as good as diagnoses made based on PET scans or spinal taps.”
Nearly 7 million people in the U.S. have Alzheimer’s disease. About one in five women and one in 10 men develop dementia (a group of medical conditions or disorders that result in mental decline, and diminished ability to think, remember and reason) due to Alzheimer’s. It accounts for over 60% of dementia cases.
Diagnosing Alzheimer’s disease typically consists of undergoing several tests, including a patient’s medical history, physical examination, neurological examination, cognitive, functional and behavioral tests, and sometimes specialized cognitive tests. “We would then do confirmatory tests for Alzheimer’s disease like spinal taps or brain imaging like PET scans,” says Dr. Honig. “The question is, in what scenario could we find that a blood test would be useful, either before or to supplant the specific testing that we do with spinal fluid or PET scans. If the blood test came out positive, that’s a good sign to do confirmatory tests and try to see if it really is or isn’t Alzheimer’s disease. It’s also exceedingly useful if we cannot do spinal fluid or PET scan on a patient.”
The study was conducted in Sweden but to be able to use the blood test in the U.S., it would need to be studied more closely here. “This is just one of many studies on blood tests to help diagnose Alzheimer’s disease,” says Dr. Honig. “The tests are still being studied and have been refined and improved over the last several years. They have come a long way.”
Lawrence S. Honig, M.D., Ph.D., is a neurologist at NewYork-Presbyterian/Columbia University Irving Medical Center and professor of neurology at the Columbia University Vagelos College of Physicians and Surgeons, specifically in its Department of Neurology, the Taub Institute for Research on Alzheimer’s Disease and the Aging Brain, and the Gertrude H. Sergievsky Center, where he directs the New York State funded Center of Excellence for Alzheimer’s Disease. Dr. Honig’s clinical specializations focus on Alzheimer’s disease, Lewy body dementia, frontotemporal dementia, progressive supranuclear palsy, Creutzfeldt-Jakob disease, immune-mediated encephalitis, and other disorders of nervous system aging and degeneration.