- A new blood test aids diagnosis of Alzheimer's in people who have symptoms.
- The test can reduce the need for a PET scan or invasive spinal tap.
- The test measures two proteins from human plasma that have been linked to the disease.
Without expensive or invasive tests, diagnosing Alzheimer’s disease has been largely a look at symptoms and the assessment of an expert or use of expensive and invasive tests. But that’s likely to change with news that the U.S. Food and Drug Administration has approved a blood test that helps with the diagnosis.
The test has a complicated name: The Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio. But the goal of the test, created by Fujirebio Diagnostics, is simple: Early detection of beta-amyloid plaques linked to the neurocognitive disease in adults 55 and older who are exhibiting signs and symptoms of the disorder.
“Alzheimer’s disease impacts too many people, more than breast cancer and prostate cancer combined,” FDA Commissioner Dr. Martin A. Makary said in a news release. “Knowing that 10% of people aged 65 and older have Alzheimer’s, and that by 2050 that number is expected to double, I am hopeful that new medical products such as this one will help patients.”
The test measures two proteins from human plasma — forms of tau and amyloid — which have been linked to the disease, calculating a ratio that “is correlated to the presence or absence of amyloid plaques in the patient’s brain, reducing the need” for an expensive positron emission tomography (PET) brain scan, which not only costs a lot, but exposes one to radiation.
The other option, a lumbar puncture, or spinal tap, is sometimes used to look at cerebrospinal fluid to detect the presence of beta-amyloid.
The new test relies on a simple blood draw.
How the new test works
As Deseret News has reported, blood tests can speed recruiting for research, reduce wait times and make access to treatments easier.
The data used to win FDA approval included a comparison of findings from 499 individual plasma samples taken from adults who were cognitively impaired against findings from an amyloid PET scan and the spinal tap samples.
Nearly 92% of those who showed amyloid on the other tests also were positive signs of amyloid on the new blood test. Just over 97% of those with negative blood test results were also negative on the PET scan and spinal fluid test.
The test was indeterminate in fewer than 20% of the samples.
“These findings indicate that the new blood test can reliably predict the presence or absence of amyloid pathology associated with Alzheimer’s disease at the time of the test in patients who are cognitively impaired. The test is intended for patients presenting at a specialized care setting with signs and symptoms of cognitive decline. The results must be interpreted in conjunction with other patient clinical information,” according to the FDA.
The release noted the main risks are the possibility of a false positive or a false negative.
The former could cause distress, unneeded treatment for Alzheimer’s and delay in correct diagnosis. The latter could delay treatment for Alzheimer’s at a time when early treatment yields the best results for certain medications, including Leqembi, which slows progression of the disease.
An aid to diagnosis, not an answer
“Importantly, the Lumipulse G pTau217/ß-Amyloid 1-42 Plasma Ratio is not intended as a screening or stand-alone diagnostic test and other clinical evaluations or additional tests should be used for determining treatment options,” per the FDA.
There is no cure at this time, but recent treatments have slowed progress, making early detection vital.
The new test was granted “breakthrough device” designation, meaning that it aids “more effective treatment or diagnosis of life-threatening or irreversibly debilitating diseases or conditions.” It was granted approval through the pathway that says a new submission is “substantially equivalent” to an already authorized device — in this case, the test that uses a spinal tap and cerebrospinal fluid samples.