New Alzheimer’s Blood Tests Are Easy. But Do You Really Want One?

The Limits Of Tests

Keep in mind what these tests can, and cannot, do. They look for biomarkers, the presence of material in the brain associated with Alzheimer’s disease, called p-tau 217 and beta amyloid.

In other words, they can show that someone has a high level of one or both of these proteins. Does that mean they have Alzheimer’s? Not exactly. Rather, it means that they have a higher risk for developing symptoms of the disease at some time in the future

Remember too that these tests are appropriate only for people with mild cognitive impairment that a physician suspects could be early Alzheimer’s. For these patients, they may provide valuable evidence that their symptoms are indeed caused by Alzheimer’s rather than some other condition. They say nothing about other forms of dementia.

It is a bit, though not quite, like a blood test that shows you have high cholesterol. That puts you at greater risk for heart disease. But it doesn’t mean you inevitably will have a cardiac event.

With Alzheimer’s, predicting the future is even murkier. That’s because while everyone with advanced disease has high levels of amyloid β in their brains, many people with lots of these proteins will never have symptoms.

Research scientists argue endlessly about whether this means people with biomarkers but no symptoms have Alzheimer’s disease or not. But from a patient’s perspective, if your memory, executive function, and other behavior never change significantly, do you have Alzheimer’s?

A Rising Risk, But No Certainty

A new study by Rachel Buckley of Mass General Brigham Hospital and many coauthors looked at outcomes over several years for about 2,700 people with no cognitive decline when they first tested for the tau protein. The result: Roughly 38% of those with very high levels of tau showed cognitive impairment after five years compared to 12% for those with low levels. The chances were greatest for older men with less education. And they increased over a 10-year period.

For context, 38% is very high risk. But less than four in ten is far from a certainty. Also keep in mind this study did not adjust for participants who may have had other medical conditions. Nor did it look at whether cognitive impairment was due to Alzheimer’s or some other cause.

Not A Death Sentence

And that’s where a new JAMA essay by doctors Stanley Lyndon, Lauren Behlke, and Juan Carlos Urizar comes in. It raises important questions about the ethical issues that arise when a patient receives an early diagnosis of Alzheimer’s, especially when they have only mild symptoms.

It seems that many patients respond to their early diagnosis by asking about dying. Some want to know about physician-assisted death. Others consider suicide.

The authors cite one study where “20% of cognitively normal adults with elevated amyloid-β reported they would pursue PAD if they became cognitively impaired, were suffering, or were burdening others.”

The Physicians Role

This issue will become especially important as more people have access to simple blood tests for those Alzheimer’s-related proteins. Until recently, relatively few patients were tested because the only alternatives were invasive spinal taps or costly PET scans. Besides, there were no effective medical treatments for Alzheimer’s in any event.

Now, we are approaching the time when a blood test for Alzheimer’s-related proteins can be included in the routine labs we get with our annual check-ups. We’ve learned interventions such as better diet, exercise, and social interaction can improve cognition. And new drugs may delay progression as well, though their benefits remain limited. All these advances may increase demand for the biomarker tests.

But, as Lyndon and colleagues write, there may be a high emotional cost to these tests. How should physicians help patients understand them and their results? Importantly, Lyndon and coauthors say doctors should begin a discussion even before the patient consents to a test.

That conversation should include information about their predictive limits, including how uncertain any given patient’s prognosis is, even if they test positive for high levels of the Alzheimer’s related proteins.

It is critical for patients to understand the results may suggest a higher risk of future dementia, but not a certainty. No test alone can predict how the disease may progress. And physicians also should make patients aware that a positive test can itself risk depression and anxiety.

As the authors say, “Biomarkers can clarify pathology, but they cannot write an individual’s timeline. Progression from MCI [mild cognitive impairment] to dementia varies widely; cognitive reserve, mixed pathologies, vascular disease, depression, sleep disorders, medication effects, and social supports shape trajectories. The risk is that patients may turn biological information into temporal certainty, collapsing ambiguity into catastrophic inevitability.”

Any post-diagnosis discussion also should include information about what community resources patients can tap, as well as support and skills training for family caregivers.

For example, physicians can now bill Medicare for teaching caregiving skills to family members, though few do.

A couple of years ago, I wrote about best practices for physicians when they diagnose dementia, recommended by University of Florida School of Medicine neurologist Melissa Armstrong. It included a potent mix of compassion, empathy, and practical advice.

Early diagnosis is becoming more common. Yet that tool may only add to the lack of certainty about how any individual’s disease will progress, as well as increased anxiety. In that environment, it will be up to patients and their families to ask more questions and for doctors to have better answers.