Every 65 seconds, someone in the United States is diagnosed with Alzheimer’s disease, and there are now more than 6.7 million Americans living with the disease, according to the Fisher Center for Alzheimer’s Research Foundation. This number could grow to 13.8 million by 2060. Early detection and diagnosis of Alzheimer's disease are crucial for improving the quality of care and life for individuals with the disease and other dementias, which makes news of a new blood test to screen for Alzheimer’s an exciting advancement. 

We spoke with Claudia Perez, M.D., a neurologist and physician on the medical staff at Texas Health Fort Worth and Neurocritical Care Associates – Fort Worth, a Texas Health Physicians Group practice, to learn more about these groundbreaking tests, the potential risks and concerns around them, and what this means for the future of Alzheimer’s research, detection and treatment.

Understanding the Tests

The study, published in the journal JAMA Neurology, involved testing blood for a key biomarker of Alzheimer’s called p-tau217.

“These blood tests are looking for a particular protein that becomes altered and ultimately can become toxic and lead to the changes associated with Alzheimer's Disease,” Perez explains. “This protein is phosphorylated tau or p-tau and can be present in the blood before the disease has progressed enough to when it can be picked up by clinical cognitive tests.”

Tau is a normal protein that is an essential part of stabilizing communication pathways across brain cells, or neurons. In Alzheimer’s disease, Perez notes that they typically see an accumulation of an abnormal version of the tau protein, which is the p-tau protein.

“This abnormal protein becomes sticky and creates thread-like structures called neurofibrillary tangles,” Perez explains. “These tangled structures build up and don’t allow neurons to function normally.”   

The study looked at information from 786 individuals, who were around 66 years old on average. They underwent brain scans, and spinal taps, and had their blood taken for samples.  During the data collection, some of the participants showed signs that their thinking abilities were getting worse, but others didn't. The researchers, who were from Sweden, the United States, and other countries, analyzed all this information from February to June of 2023.

The researchers discovered that when they tested a participant’s blood sample with the p-tau217 immunoassay, the results were very similar to those obtained from the person's spinal tap or brain scan. This means the blood test was just as good at finding abnormal beta-amyloid and tau in the brain.

Interestingly, only around 20% of the people in the study had blood test results that might need further testing with imaging or a spinal tap because they weren't entirely clear.

The Positives

Currently, to identify the buildup of beta-amyloid and tau in the brain, patients need to have a brain scan or a spinal tap. These tests can be hard to get and expensive.

But this simple blood test was found to be up to 96% accurate in identifying elevated levels of beta-amyloid and up to 97% accurate in identifying tau.

“Blood tests can mean easier testing, which can allow diagnosis in a larger group of patients and identification of patients who are in the pre-clinical phase, those who are at high risk for developing the disease but do not have clinical symptoms yet,” Perez says. “The other advantage of these blood tests is that they may allow easier tracking of these levels across the progression of the disease. In those patients who are undergoing treatment, this can allow tracking of changes in tau and may allow us to track treatment effectiveness.”

The Potential Drawbacks

Despite the blood test's high accuracy in predicting key Alzheimer's disease characteristics in the brain, it's important to note that not everyone with these characteristics will actually develop the disease. In other words, while the test can spot potential signs of Alzheimer's, it can't guarantee who will definitely develop it.

“The goal would be to use these tests along with a clinical examination to allow for tracking the development or progression of disease,” Perez adds.

Additionally, Perez notes it's crucial to understand that the p-tau test specifically targets Alzheimer's disease. So, if someone tests negative but is still experiencing cognitive issues, this test won't be able to identify other potential causes of their symptoms, like vascular dementia or Lewy body dementia. This means that a negative result doesn't rule out all forms of dementia, and further evaluation may be needed to pinpoint the exact cause of the cognitive impairment.

What This Means for the Future of Alzheimer’s Detection and Treatment

Overall, a blood test for Alzheimer’s disease can be used as a valuable diagnostic tool. It enables the identification of individuals experiencing early memory loss and even those who haven't yet displayed any noticeable signs or symptoms of the disease.

This is significant because alterations in the brain associated with Alzheimer's can manifest up to 20 years prior to the appearance of obvious symptoms. Therefore, by detecting these changes early on through the blood test, health care professionals can initiate timely interventions and treatment strategies, potentially leading to better outcomes for those at risk of developing Alzheimer's disease.

“Some of the newer treatments for Alzheimer’s, have centered around treating patients who are already in an early phase of cognitive impairment and mild dementia, to slow down the progression of disease,” Perez explains. “The newer drugs are aimed at clearing abnormal proteins, so if we can identify more patient when p-tau has not caused significant damage and clear it early, we might be able to slow the progression to more severe disease. This test might allow us to identify patients who are at high risk for developing clinical symptoms and may lead to future strategies to help prevent the disease from progressing or occurring at all.”

Signs and symptoms of Alzheimer's disease can differ from person to person, but memory problems are often the initial indicators. These may include difficulty remembering dates, getting disoriented or lost in familiar places, misplacing items frequently, or struggling to complete everyday tasks like bathing, reading, or writing. These early signs can gradually worsen over time, impacting various aspects of daily life and eventually leading to more severe cognitive decline.

Perez hopes that in the future, blood tests like the ones discussed in the study can be utilized in primary care practices and included in regular screenings, such as those for cholesterol or diabetes.

“I can see how this test may be a powerful screening tool early on in family medicine or primary care offices, which can allow for early identification of pre-clinical patients and can lead to an earlier diagnosis to help start treatments early on,” she adds.

While we will still have to wait for more research on the safety and efficacy of these blood tests, Perez notes there are some things you can do right now to help prevent Alzheimer’s Disease and other dementias. Although there is no definitive way to prevent Alzheimer's disease, several strategies may help reduce the risk:

• Healthy Lifestyle: Leading a healthy lifestyle, including being physically active, maintaining a balanced diet, and controlling cardiovascular risk factors, may help reduce the risk of Alzheimer's disease and other types of dementia.
• Physical Activity: Although no clear link between physical activity and preventing Alzheimer's has been documented, preliminary research suggests that it may help reduce the risk of age-related cognitive decline.
• Cardiovascular Health: Improving cardiovascular health through measures such as controlling blood pressure, maintaining a healthy diet, and engaging in regular physical exercise may contribute to reducing the risk of Alzheimer's disease and vascular dementia.
• Mental and Social Activity: Staying mentally and socially active throughout life, such as reading, learning new skills, and maintaining an active social life, may help reduce the risk of Alzheimer's disease and other types of dementia.