New Blood Test for Alzheimer’s Highlights Needs to Treat the Patient, Not the Disease

By Alvaro Pascual-Leone, MD, PhD

Progress against Alzheimer’s disease has been so halting that each new advancement is greeted with an understandable flurry of hope and hyperbole.

Our eagerness to see Alzheimer’s defeated is understandable. We fear it because it is the most common cause of dementia, and dementia erases our essence, robs us of our memories, and turns loved ones into strangers. The lack of a cure or even an effective treatment increases our dread. However, to be clear, what terrifies us are the potential consequences of Alzheimer’s, not the disease itself. What we fear is dementia, not Alzheimer’s.

Now, there is a new advance, a blood test that can screen for Alzheimer’s disease biomarkers by detecting changes in amyloid beta and tau protein levels in the brain, potentially years before symptoms emerge. This breakthrough marks significant progress in diagnosing the disease, which now requires testing cerebrospinal fluids or PET scans. More accessible testing could allow drug therapy to begin at earlier stages of the disease, potentially with better outcomes.

Not surprisingly, news of the test is generating dialogue that could mislead the public about the actual state of progress against the disease and what it can accomplish. Many public misperceptions about Alzheimer’s stem from confusion over what the disease actually is, its relationship with dementia, and what a blood-based biomarker test can show. Physicians should treat the patient, the person and their circumstances afflicted by a disease, not the disease itself. With this in mind, the following facts put the latest developments into perspective:

Not every patient with dementia has Alzheimer’s. Though it is the best-known and most common cause, Alzheimer’s is only one cause of dementia and is responsible for about half of dementia cases. Increasingly, we have come to learn that often more than one cause contributes to a given patient’s dementia. The new blood test is not relevant for other causes of dementia, such as vascular dementia and Lewy Body dementia.

Not everyone with Alzheimer’s has dementia. Having Alzheimer’s disease does not automatically equate to having dementia or any sort of cognitive impairment. Approximately 20% to 25% of people with Alzheimer’s do not experience dementia. In most cases, they are unaware they have it. Others with the disease have the ability to slow down progression of the clinical manifestations of the disease, remain in a mild cognitive impairment state, and prevent or delay the development of dementia.

Blood-based biomarker tests do not indicate dementia. A blood test that detects elevated levels of amyloid beta and tau protein in the brain does not actually confirm anything other than the existence of those levels and arguably a given pathology in the brain. It does not mean that the patient has dementia or will develop dementia.

Widespread use of the blood test could be unnecessarily alarming. Communicating an Alzheimer’s diagnosis to a patient is important, but many physicians fail to do so. Delivering the results of a blood test that confirms abnormal levels of amyloid beta and tau protein but doesn’t really address the question of cognitive impairment or dementia is likely to be even more problematic. It could unnecessarily panic and distress patients, and now we know that increased worries, negative thinking and lack of hope can increase the risk of dementia and worsen a patient’s condition.

Cognitive testing is required for accurate diagnosis and staging. We dread dementia, and what we fear about Alzheimer’s is that it often, though not always, leads to dementia. Biomarker tests do not address cognitive function or dementia, and Alzheimer’s without dementia may not affect an individual’s cognitive function, wellbeing and behavior.

Identifying individuals with mild cognitive impairment (MCI), a precursor to dementia, is tricky. Over 90% of patients with MCI are thought to be undiagnosed. Even though the majority of people would like to get tested and primary care providers agree early detection would be important, fewer than 30% of them routinely screen their patients. Instead, they wait for patients or a family member to raise concerns. And traditional paper-and-pencil screening tests are not sensitive enough to detect the earliest signs of cognitive difficulties, are open to misinterpretation, and take too long to administer.

This means dementia care is reactive, and diagnosis and treatment considerations come years too late. Fortunately, newer digital screening tests that can be completed in a few minutes on a tablet in a primary care physician’s office can accurately detect cognitive impairment before traditional tests would. Ideally, these screenings would be performed in conjunction with blood biomarker testing—so if someone is showing signs of MCI, they would be referred for blood testing.

To accurately determine the stage of the disease it’s necessary to know three things about a patient with Alzheimer’s: their amyloid and tau and brain degeneration status to know whether they have Alzheimer’s, their extent of cognitive impairment, and how well they perform daily activities to know whether they have MCI or dementia. A biomarker test provides only the first; cognitive screenings measure the other two and can predict the likelihood of the first.

Progress against Alzheimer’s is real and exciting. But to help patients and their families and friends as we advance, it’s important to further public knowledge of the disease and to understand what each new therapy and test can accomplish. Most importantly, we need to keep in mind that the goal is not to treat the disease, but to treat the person.

Alvaro Pascual-Leone, MD, PhD, is a Professor of Neurology at Harvard Medical School, a Senior Scientist at the Hinda and Arthur Marcus Institute for Aging Research, and the Medical Director of the Deanna and Sidney Wolk Center for Memory Health at Hebrew SeniorLife (HSL) in Boston. He is also co-founder and chief medical officer of Linus Health. A major focus of his scientific work is to characterize and promote brain health across the lifespan, prevent age-related cognitive decline, and minimize disability in patients with neuropsychiatric disorders while gaining fundamental insights into human brain function.