Study finds blood test diagnosed Alzheimer's disease 90% of the time; early diagnosis is crucial with new medications available

2024 Alzheimer's disease facts and figures
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By Melissa Patrick
Kentucky Health News

A blood test can diagnose Alzheimer's disease better than a memory specialist or a primary care physician, according to a new study. 

The study, published in the Journal of the American Medical Association, found that the blood test, called PrecivityAD2, was 90% accurate in diagnosing Alzheimer's disease, compared to a 61% success rate among primary care doctors and a 73% success rate among memory specialists. All of the physicians used standard clinical methods for diagnosis that did not include brain scans or spinal taps. 

The researchers at Lund University in Sweden followed 1,213 people with an average age of 74 who were undergoing cognitive evaluations in both primary care and specialty clinics in Sweden.

Dr. Greg Cooper, director of the Norton Neuroscience Institute Memory Center in Louisville, explained that there are protein biomarkers that are indicative of Alzheimer's disease and can be identified through a a spinal tap, which is invasive, or a brain scan called a PET scan, which he said are not always available, are expensive and are not well-covered by insurance. 

But now, he said, there is a blood test that can accurately detect these biomarkers. The blood test works by measuring a combination of two ratios within a blood sample, including the phosphorylated tau protein and two amyloid-beta proteins, both considered  hallmarks of Alzheimer's disease. 

"Most people would prefer a blood test over a spinal fluid exam, a spinal tap," he said. 

Cooper added that the blood test should be used only on people who show signs of memory loss or have a diagnosis of mild cognitive impairment or dementia. In this group, he said, "It is a very accurate test." 

Further, he said this blood test will help people get an early diagnosis, which is needed to qualify for the two new drugs approved to modestly slow the symptoms of Alzheimer's: Leqembi and Kisunla. At this time, Cooper said it can take months or even years before a person can receive a diagnosis. 

"As newer medications become available . . . we need to do a better job of identifying people very early on, when they are the best possible candidates for these medications that we believe actually slow the progression of the disease."

According to the Alzheimer's Association, nearly 7 million Americans are living with Alzheimer’s disease, with this number projected to rise to nearly 13 million by 2050. In Kentucky, the association reports that 81,000 people aged 65 and older are living with Alzheimer's.

Cooper said the Norton memory center is already using this blood test, but there remains some barriers. 

"The biggest barrier right now has been in terms of payments," he said. "So we are using this exact same test that was used in this study and the results are really quite good. But payment is an issue.

Insurance does not always cover this and so there is often an out-of-pocket expense."

He said he is hopeful that with studies like this one and future U.S. Food and Drug Administration approval, insurance will eventually pay for it. " I think it is only a matter of time before insurance starts paying for it, "he said. "At this time, it's just simply too new." 

He said it "remains to be determined" if primary care doctors should do this blood test, largely related to their ability to do cognitive memory testing in their practices. With the advent of these new medications that require early diagnosis, he said there is a sense of urgency to diagnose people early on and a patient's first point of contact is often their primary care provider. 

"The worst thing in the world is to tell someone had I seen you six months or a year earlier, you might have been a candidate for one of these new treatments -- and now you're not," he said. "Tests like this will help accelerate that process and allow more people to benefit from these therapies."

Recognizing that many people are afraid of getting an Alzheimer's diagnosis, Cooper said: "I would simply argue that not receiving a diagnosis, if you have that underlying disease, doesn't make the disease go away. You can't ignore it. It will catch up with you eventually. But now, we have opportunities to take a proactive approach. Maybe we can't cure it, but we can do things that meaningfully impact the disease and can meaningfully impact and promote our quality of life. So it is an awful diagnosis, I can't take that away. But we can't help unless we take that first step. And so always keep in mind, there may be things that we can do. Don't run away from that."