A recent study indicated that a combined blood test for cognitive decline may accurately identify 90% of cases of memory loss as being caused by Alzheimer’s disease.

By contrast, 73% of cases diagnosed with Alzheimer’s disease by neurologists and other memory specialists were accurately diagnosed. The study found that primary care physicians performed even worse, with an accuracy rate of just 61%.

One component of the blood test, known as plasma phosphorylated tau 217, or p-tau217 for short, is being studied by scientists as one of numerous blood biomarkers for the identification of Alzheimer’s disease at an early stage and mild cognitive impairment.

The test quantifies tau protein 217, a highly reliable marker of amyloid disease, according to study coauthor Dr. Sebastian Palmqvist, a senior consultant neurologist at Lund University in Sweden and associate professor.

“Paint tau-217 blood concentrations rise significantly in Alzheimer’s disease patients. In comparison to senior people without Alzheimer’s disease, levels are more than eight times higher in the dementia stage of the disease, according to an email from Palmqvist.

A related test called p-tau217 is up to 96% accurate in detecting high levels of beta-amyloid and up to 97% accurate in identifying tau, according to research published in January. The brain’s beta-amyloid and tau tangles are characteristic indicators of Alzheimer’s disease.

The p-tau217 test was used in the latest study in conjunction with the amyloid 42/40 ratio, a blood biomarker of Alzheimer’s disease that detects two different forms of amyloid proteins.

The most predictive was the amyloid likelihood score, which was derived from the combination of the tau and amyloid tests.

The Alzheimer’s Association’s chief science officer, Dr. Maria Carrillo, stated, “We’d love to have a blood test that can be used in a primary care physician’s office, functioning like a cholesterol test but for Alzheimer’s.”

“The p-tau217 blood test is turning out to be the most specific for Alzheimer’s and the one with the most validity. It seems to be the front-runner,” according to Carrillo, the association’s research project coordinator, who also provided some funds for the recent study.

High-accuracy blood tests have the potential to “change the game in the speed at which we can conduct Alzheimer’s trials and get to the next new medication,” she said, once they have undergone thorough testing.“These are absolutely transformational times.”

How does a blood test for p-tau217 operate?

According to Carrillo, p-tau217 is a unique peptide that is only seen in the brain when amyloid plaques are present.

“What that means to us scientifically is that when we’re measuring p-tau217, we’re measuring the neuronal damage from tau very early on in Alzheimer’s, but only when amyloid is already present,” the speaker explained.

“You’re not really measuring amyloid, but the test is telling you it’s there, and that’s been backed up with objective PET (positron emission tomography) scans that can see amyloid in the brain,” explained Carrillo. “It’s a beautiful marker for Alzheimer’s: If you don’t have amyloid present, you don’t have Alzheimer’s. If you have elevated tau in your brain, however, then we know that’s a sign of another type of dementia.”

Frontal lobe dementia, or FTD, is one of the neurological conditions that tau tangles have been linked to. The frontal lobe of the brain is attacked by tau tangles in frontal lobe dementia (FTD), which results in behavioral, affective, and executive function loss, including planning. If memory loss develops, it does so considerably later.

Although amyloid plaques are a major factor, tau tangles accumulate in the area of the brain that controls memory in Alzheimer’s disease. At synapses, tiny clusters of plaques can form and obstruct communication between nerve cells. Additionally, amyloid plaques have the potential to overstimulate the immune system, resulting in inflammation and additional brain injury.

Experts believe that some of the newest medications for dementia, such lecanemab and donanemab, which target beta-amyloid, are less effective in patients with extensive tau pathology.

Even in people in their 30s or 40s, deposits of amyloid can start to build up in the brain decades before symptoms appear, so early detection of brain amyloid may be essential for preventive pharmaceutical treatment and lifestyle changes.

The screening tests used now are not conclusive

The research, which was released on Sunday in the journal JAMA Neurology, tracked 1,213 subjects in Sweden who were having cognitive assessments performed in primary care and specialized clinics. The subjects’ average age was 74.

A final score was calculated by combining blood measurements of beta-amyloid 40/42 with the findings of each individual’s p-tau217 test.

“When you use a combination of the 40 to 42 ratio and p-tau217, it increases the diagnostic accuracy of p-tau217,” stated Dr. Richard Isaacson, director of research at the Institute for Neurodegenerative Diseases in Florida and preventive neurologist, who was not involved in the study.

A spinal fluid tap was used to verify the study’s combined blood test’s 90% accuracy. This test, together with an amyloid PET scan, is presently the only gold-standard scientific approach for detecting Alzheimer’s disease outside of autopsy. Experts claim that both tests are pricy, intrusive, and not easily accessible across the United States.

Following that, the blood test results were compared to the patient diagnoses given by Swedish primary care physicians and specialists. The comparatively low accuracy rates (61% and 73%) demonstrate how challenging it is for medical professionals to diagnose Alzheimer’s pathology accurately using the current diagnostic methods, which include a quick cognitive test, a brief patient interview, and a computed tomography, or CT, scan of the brain.

“Generally, both traditional paper-and-pen tests and digital cognitive assessments are not highly accurate in specifically identifying Alzheimer’s disease,” according to research coauthor Dr. Oskar Hansson, a senior consultant in neurology at Lund University and professor.

In an email, Hansson stated, “Many other conditions and diseases can present similar cognitive symptoms, leading to potential misdiagnosis or missed diagnosis.”

According to Hansson, between 20% and 30% of people who consult specialists have other medical issues or are on drugs that can mimic Alzheimer’s disease. Conditions including vascular dementia, depression, thyroid issues, sleep apnea, and even a vitamin B12 deficiency can all have an impact on cognitive performance.

People without Alzheimer’s pathology may backlog appointments for spinal taps and amyloid PET scans as well as specialist waiting lists if those mimics are missed during the initial assessment, according to Carrillo.

She continued by saying that a person with real amyloid pathology can “fall out of that window of being eligible for the drugs we have, and that’s terrible” by the time they see a specialist.

When will it be possible to get regular blood tests?

However, the study revealed that wait times may decrease to six to thirteen months if correct blood tests were employed, as fewer people would require follow-up testing or consultation with specialists.

It is unlikely that routine blood testing for Alzheimer’s will soon be available at the office of your primary care physician.

However, don’t anticipate seeing routine blood tests for Alzheimer’s in the office of your general care physician anytime soon. According to Isaacson, more study is required to confirm the encouraging findings seen in studies, recommendations for physician use need to be created and disseminated, and doctors need to be informed about any potential subtleties.

He stated, “There’s no one more bullish on these tests than I am, but Alzheimer’s blood tests aren’t fully definitive yet,” “If it is a positive test, it still needs to be confirmed via PET scan or spinal tap. If it’s a negative result, that’s reassuring, but if it’s borderline, we still don’t know what that means.”

A Mediterranean-style diet, frequent exercise, and managing vascular risk factors like high blood pressure, high cholesterol, and diabetes are just a few of the steps people can take to avoid or delay cognitive impairment in the interim.

“It’s our goal to use only the highest-quality blood tests to not only help make an early diagnosis of Alzheimer’s but also evaluate response to risk-reducing interventions,” Isaacson stated. “These are very hopeful times.”