Researchers at Washington University have developed a blood test for Alzheimer's disease that can detect beta amyloid—a protein that accumulates and creates plaques in the brain, which are predictors of Alzheimer's— in asymptomatic patients and might be more sensitive than a PET brain scan, according to a paper published recently in Neurology.
Why Alzheimer's is hard to diagnose
There currently is no blood test that detects Alzheimer's disease, and it is difficult for doctors to diagnose patients with the condition.
While PET scans are considered the gold standard for diagnosing Alzheimer's disease, the tests can be costly and they are not always available to patients. As such, doctors usually rely on mental acuity tests and interviews with patients and their families to diagnose the disease, the New York Times reports. Research shows that community doctors are only 50% to 60% accurate in diagnosing Alzheimer's disease.
To improve accuracy, scientists have spent decades trying to develop a blood test that is sensitive enough to detect beta amyloid, a protein that accumulates and creates plaques in the brain, which are predictors of Alzheimer's.
The new test
Researchers from Washington University developed such a test and conducted a study to determine whether it could detect beta amyloid in patients' brains. For the study, the researchers observed 158 participants, most of whom were "cognitively normal" individuals in their 60s and 70s. The participants underwent memory and reasoning tests, as well as spinal taps and amyloid PET scans.
The researchers then used mass spectrometry, a tool that can detect beta amyloid molecules in blood, to test the patients' blood for the beta amyloid protein within 18 months of receiving a PET scan. Suzanne Schindler, a neurologist and one of the main authors of the study, explained that low levels of the beta amyloid protein in a patient's blood mean the patient is more likely to have plaques in the brain that are associated with Alzheimer's disease.
The blood test confirmed the results of the participants' PET scans 88% of the time, according to the study. Further, when researchers combined the blood test's results with other risk factors for Alzheimer's—including age and the presence or absence of the gene variant ApoE4—the researchers found that the blood test was 94% accurate in predicting the presence of amyloid plaques in a participant's brain.
The researchers also found that mass spectrometry was able to identify accumulations of beta amyloid in asymptomatic patients, even when the patients' PET scans did not show a buildup of the protein. According to the researchers, the PET scans did not detect beta amyloid in the patients' brains until years later.
The test is not yet accurate enough to be used as a clinical diagnostic test, and will not be available for use in a clinical setting for at least a few years, the researchers said. They explained that beta amyloid is still not a perfect predictor of the condition. Most asymptomatic older patients with amyloid deposits do not develop dementia, the Times reports.
Still, the blood test likely is the most sensitive Alzheimer's test yet, and it could help researchers working to prevent Alzheimer's, according to the Times.
Michael Weiner, a neurologist at the University of California, San Francisco, said the test could be particularly helpful to scientists seeking patients in the earliest stages of Alzheimer's in order to conduct a clinical trial on Alzheimer's prevention drugs.
Randall Bateman, a neurology professor at Washington University and senior author of the paper, explained, "Right now we screen people for clinical trials with brain scans, which is time-consuming and expensive, and enrolling participants takes years." He added, "But with a blood test, we could potentially screen thousands of people a month" (Kolata, New York Times, 8/1; Bhandari, Science Daily, 8/1; WDRB, 8/4).