Understanding The New Alzheimer’s Disease Blood Test And How It Works

A new blood test for Alzheimer’s disease may feel like a breakthrough for anyone seeking to understand the cause of their fading memory or that of a loved one. By measuring Alzheimer’s disease-related proteins in the blood, the test provides important information more easily than current methods of making a diagnosis. Experts emphasize, however, that the test is not a shortcut. It is ordered only when a healthcare professional, after carefully evaluating symptoms, strongly suspects Alzheimer’s disease. Right now, it’s not meant for general screening or for people simply worried about occasional forgetfulness.

A simpler way to identify Alzheimer’s changes in the brain

Alzheimer’s disease begins years — even decades — before symptoms appear. During that time, proteins such as beta-amyloid and tau start to build up in the brain. This buildup leads to nerve cell damage and, eventually, memory loss and cognitive decline.

“Alzheimer’s starts with changes in brain proteins that eventually damage brain cells and cause symptoms,” says Gregg S. Day, M.D., a neurologist, dementia specialist and clinical researcher at Mayo Clinic in Jacksonville, Florida.

Until recently, confirming changes related to Alzheimer’s disease required either a lumbar puncture, also called a spinal tap, or a PET scan. A spinal tap looks for these specific proteins, known as biomarkers, in the cerebrospinal fluid — the clear liquid that surrounds and cushions the brain and spinal cord. These biomarkers reveal what’s happening in the brain. PET scans, on the other hand, use special tracers to show whether amyloid plaques — clumps of the beta-amyloid protein — are accumulating in the brain.

Both tests are accurate but far from convenient. People find spinal taps to be invasive, says Dr. Day. And PET scans, while not invasive, are not available everywhere and can cost tens of thousands of dollars.

The new test measures the same disease-related processes through a simple blood draw. “This test serves as a surrogate marker to assess that accumulation of beta-amyloid in the brain,” says Alicia Algeciras-Schimnich, Ph.D., a consultant in the Division of Clinical Biochemistry and Immunology at Mayo Clinic. Dr. Algeciras-Schimnich is also a professor of laboratory medicine and pathology at Mayo Clinic College of Medicine and Science. That simplicity could transform access to Alzheimer’s disease testing.

“Anywhere there’s a phlebotomist — a person trained to draw blood — you can go to have a blood sample collected,” Dr. Algeciras-Schimnich says. The sample is then sent to one of many reference laboratories that can perform the test.

Insurance coverage for the new blood test varies. “Coverage is going to be dependent on the state and what the arrangements are between private insurance, hospitals, and Medicare or Medicaid,” says Dr. Algeciras-Schimnich. Some people may find the test is covered, while others may not.

In studies at Mayo Clinic, the test has shown impressive reliability, with over 90% accuracy in detecting changes related to Alzheimer’s disease in research participants and clinic patients with memory concerns. That meets the Alzheimer’s Association’s criteria for the use of a blood test to determine amyloid protein accumulation and potentially replace the spinal fluid biomarkers, Dr. Algeciras-Schimnich says.

What a positive Alzheimer’s disease blood test means

A positive result can be deeply unsettling. It confirms that Alzheimer’s-related proteins are present. But that finding alone doesn’t mean a person has the disease, says Dr. Day. He adds that some people need additional interpretation of their blood test results. That’s especially true of people who have changes in kidney function. Because the kidneys help remove proteins from the blood, poor kidney function can cause the proteins measured by the test to appear falsely elevated. This means a positive result does not always indicate Alzheimer’s disease, and healthcare professionals should consider kidney function and other health factors when interpreting results.

And according to Dr. Day, Alzheimer’s-related changes can exist in the brain even when they aren’t the cause of a person’s symptoms. “The older our patients are, the more likely they are to potentially have one, two or three different things going on that may all together be contributing to their memory problems,” he says. “So we can see patients who, yes, there are changes of Alzheimer’s disease and yes, it’s a positive blood test, but it’s not actually Alzheimer’s that is causing their symptoms.”

That’s why a full evaluation and follow-up with an experienced clinician are so important. A blood test may offer information, but it doesn’t replace a thoughtful conversation with a healthcare professional — or the time and care needed to process what the results mean.

If you or a loved one receives a positive result, the next step typically is confirmation with a spinal tap or PET scan. These remain the gold standard tests for Alzheimer’s, Dr. Day says.

After the diagnosis is confirmed, you will want to have a careful discussion about treatment options with the care team. Some Alzheimer’s disease therapies can involve long-term infusions and carry potential side effects. “We’re still using those gold standard tests to confirm the diagnosis before we start therapies that are very involved and have the potential for risk,” Dr. Day says.

The role of blood tests in Alzheimer’s disease treatment

At least for the near future, the test is unlikely to change the approach to treatment, Dr. Day says. “These tests should only be ordered by a physician who knows how to interpret the results and who has completed a comprehensive assessment of the patient,” he says.

Eventually, however, blood tests could help detect Alzheimer’s before symptoms appear. An early diagnosis could help healthcare professionals intervene to prevent symptoms from developing — provided there are effective treatments available. “We need to have treatments that are proven to reduce the emergence of symptoms in cognitively normal people,” Dr. Day says. Researchers are continuing to look for new Alzheimer’s treatments.

Blood tests also may be useful one day for monitoring response to Alzheimer’s treatment.

The new blood test is a major step forward — offering more-accessible, accurate information. It represents real progress in understanding, diagnosing and ultimately treating Alzheimer’s disease.

But experts stress it is a tool, not a definitive answer.

“Just because we have a blood rest, it doesn’t mean that if the test is abnormal, you have the disease,” Dr. Algeciras-Schimnich says. “There is always the possibility that there is a false positive result because of the decreased kidney function or for some analytical reasons that we’re still trying to learn.” As with all new tests, she says, “we need to get familiarized and test many samples to fully understand their performance long term.”