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A new blood test found Alzheimer’s disease just as accurately as an expensive brain scan or spinal canal, increasing the possibility of a new, inexpensive way to diagnose the most common form of dementia, the researchers said.

Researchers at the International Conference of the Alzheimer’s Association on Tuesday presented the results of numerous studies on whether blood tests can distinguish Alzheimer’s disease from other forms of dementia.

In one study published in JAMA, researchers said a blood test could detect Alzheimer’s disease and even show signs of the disease 20 years before cognitive problems were expected in a group of people with a rare genetic mutation.

Blood tests to detect Alzheimer’s disease at an early stage may be more accurate than the memory and thinking tests currently used to diagnose the disease. Invasive and expensive brain scans and spinal taps that measure spinal fluid are used, but insurance does not always cover these tests.

The researchers reported that a blood test measuring tau protein accurately distinguished Alzheimer’s disease from other forms of dementia in 89% to 98% of cases.

“It’s a promising blood test that seems to be very accurate and seems to detect (Alzheimer’s) relatively early,” said Dr. Eric Reiman, a research fellow and executive director of the Banner Alzheimer’s Institute in Phoenix.

But experts have warned that it may take several years for both doctors and researchers to confirm a blood test as a reliable option. And would patients want to know that they are destined to develop memory and thinking problems if there is no reliable cure for the deadly disease?

Randall J. Bateman, a professor of neurology at the University of Washington and an Alzheimer’s researcher, said blood tests could be useful for both patients and doctors, as well as scientists studying new drugs to slow the disease that excites the mind.

Physicians can use the test to accurately diagnose Alzheimer’s disease earlier and begin treatment with existing approved foods and medications that relieve symptoms, if not mental reduction.

But perhaps more benefit will come from accelerating research into new drugs that seek to slow or stop the disease, which affects 5.8 million older Americans. Drug companies have been developing amyloid protein therapy for decades, a theory responsible for blurring memory and thinking in Alzheimer’s patients. Some recent studies have sought to introduce drugs that target these proteins before problems with memory and thinking.

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Bateman said such blood tests, which detect Alzheimer’s disease before symptoms appear, would “become transformational” for studies that try to stop or slow the disease.

“If we can prevent these symptoms, that’s why we’re so excited about these types of biomarkers,” he said. “And we believe that in the right combination, these biomarkers for blood will also tell us when someone gets sick. It will be very useful in the clinic when we train these patients.”

Dr. Oscar Hanson of Lund University in Sweden led the study of the Eli Lilly test, which measures tau protein in more than 1,400 people already enrolled in dementia studies in Sweden, Arizona and Colombia. These included people without impairment, mild impairment, Alzheimer’s disease and other neurological diseases.

The p-tau217 test preceded a number of other measures to indicate which patients had Alzheimer’s, as confirmed by brain scans. This was also compared to a brain scan and some spine tests for accuracy.

The Arizona portion of the study included 81 people who donated their brains after death, so the researchers were able to show that blood tests while they were alive were consistent with evidence of the disease later.

The Colombian part of the study included people with a rare genetic mutation that ensures that they will develop Alzheimer’s disease at a young age, usually in their 40s. In those with the gene, blood levels of p-tau217 began to rise “about 20 years before symptoms appear,” Hanson said.

The associate press contributed

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