The Food and Drug Administration (FDA) cleared the first blood test recently to help diagnose Alzheimer's disease.
The test, manufactured by Fujirebio Diagnostics, is for those aged 55 and older who are already exhibiting signs and symptoms of the disease, the agency said.
Alzheimer's disease is a neurodegenerative disorder that gradually destroys memory and thinking skills. It is often characterized by amyloid plaques, which are clumps of protein that can be seen as dark spots in certain brain scans.
The new blood test works by measuring the ratio of two proteins -- pTau217 and β-amyloid 1-42 -- which are found in human plasma, a component of blood. That ratio is then linked to the presence or absence of amyloid plaques in the brain to determine whether a patient is showing signs of Alzheimer's disease.
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More than 91% of nearly 500 cognitively impaired patients in a clinical study, who received a positive result on the blood test, had their results confirmed with other diagnostic tools. More than 97% of participants had their negative tests accurately confirmed.
The new test could help patients begin the diagnosis process in a less invasive and more accessible way than what was previously available.
Typically, an accurate Alzheimer's diagnosis requires expensive and time-consuming testing, including a brain positron emission tomography (PET) scan, which is a type of imaging test of the brain. Another procedure, known as a spinal tap, which draws fluid from the spine, can also be used.
"This blood test will allow primary care providers to start the diagnostic process, which is meaningful because patients typically wait months to be evaluated by a neurologist," Dr. Leah Croll, an assistant professor of neurology at SUNY Downstate Health Sciences University, told ABC News.
Positive test results will likely still require further testing, and a provider will need to rely on other clinical information to accurately diagnose a patient.
The main risk of the blood test is the possibility of a false positive or false negative, the FDA noted.
False positives were also a concern for Croll. "The thought of Alzheimer's is enough to trigger significant levels of worry and distress," she said.
False negatives, on the other hand, may result in unnecessary additional testing and delays in treatment. The new blood test should not be intended as a stand-alone diagnostic test, the FDA said. Other clinical tests should be used for determining treatment options, the agency added.
There are currently multiple drugs available to treat mild to moderate Alzheimer's, making an early and accurate diagnosis an important first step to managing symptoms and slowing further cognitive decline.
"Now that we have drugs that work for early Alzheimer's, getting early and accurate diagnosis is more important than ever," Croll said.
Nearly 7 million people in the U.S. have Alzheimer's disease, according to the Centers for Disease Control and Prevention. That figure is expected to double by 2060, the CDC says.
