A Blood Test Accurately Diagnosed Alzheimer's 90% of the Time, Study Finds

Scientists have developed a blood test that accurately identifies Alzheimer's disease in patients with memory issues 90% of the time (source may be paywalled; alternative source), significantly outperforming standard diagnostic methods. The findings have been published in the journal JAMA. The New York Times reports: The new study used a blood test that focuses on a form of a protein called tau that sprouts into tangles in the brains of people with Alzheimer's. Measuring that form, called ptau-217, was found to give the most accurate assessment of Alzheimer's pathology in a comparison of various Alzheimer's blood tests that will also be presented at the Alzheimer's Association conference. Tau is more closely linked to cognitive decline than amyloid, and tau tangles form later than amyloid plaques in Alzheimer's patients. The test in the study also tracks amyloid. Tests like this are available in the United States for use by doctors, not consumers.

The study included about 1,200 patients with mild memory problems. About 500 of them visited primary care physicians; the rest sought specialist care at memory clinics. Dr. Sebastian Palmqvist, an associate professor of neurology at Lund University who led the study with [Dr. Oskar Hansson, a professor of clinical memory research at Lund University in Sweden and the senior author of the study], said that first, about 300 patients in each group were given the blood test, and results were compared with spinal taps or PET scans. Then the researchers wanted to see how the blood test compared with the judgment of doctors after they administered cognitive tests and CT scans. 'We started asking both the primary care physicians and our own dementia specialists: After the standard evaluation, do you think your patient has Alzheimer's disease?' Dr. Palmqvist said.

In evaluations of about 200 patients, primary care doctors who thought patients had Alzheimer's were wrong 36 percent of the time. And when they thought patients did not have Alzheimer's, they were wrong 41 percent of the time. Memory specialists who evaluated about 400 patients did somewhat better -- they were wrong 25 percent of the time when they thought patients had Alzheimer's and wrong 29 percent of the time when they thought patients didn't. The blood test was wrong only about 10 percent of the time. The blood test's accuracy was highest with patients who had already progressed to dementia and was slightly lower with patients in a pre-dementia stage called mild cognitive impairment, Dr. Palmqvist said. It was not very accurate with the earliest stage, called subjective cognitive decline, when patients begin to perceive their memory to be failing. Dr. Hansson said that lower accuracy probably occurred because many people with subjective cognitive decline do not turn out to have Alzheimer's.

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