But by looking at a number of different proteins in the blood, O'Bryant and colleagues have found a "biomarker profile" typical of people with Alzheimer's. By adding some basic demographic information about a patient, the test becomes even more accurate.
"In the near future, we will be able to provide a rapid, cost-effective, and accurate diagnosis of Alzheimer's disease using blood tests as well as some simple questions," O'Bryant tells WebMD. "It won't require a half day assessment in specialty clinic."
An earlier effort to develop a blood biomarker test for Alzheimer's disease showed promise in preliminary studies. But that test proved difficult to verify. O'Bryant says he's more hopeful about the current test, as samples were tested at a large commercial laboratory -- and as other researchers have begun to report results similar to his.
Indeed, the test was highly accurate at distinguishing people with Alzheimer's disease from people with no mental impairment. When combined with demographic data, it detected 94% of patients with Alzheimer's disease. However, it also had a false-positive rate of 16%.
Blood Test for Alzheimer's: Urgent Need for More Work
Nobody would be happier to see a simple blood test for Alzheimer's disease than Ralph Nixon, MD, PhD, director of the Silberstein Alzheimer's Institute at New York University. But Nixon cautions that the O'Bryant test needs more work.
"This test is not ready for the clinic at this point," Nixon cautions. "It would only add a modest amount of support to the currently available tools we have now. But the importance of this finding is that it is one step on the path to finding a blood test that able to indicate early Alzheimer's disease with some degree of certainty."
O'Bryant notes that so far, the blood test has only been used to tell people with Alzheimer's disease from people who are mentally intact. He agrees with Nixon that the test's true test will be to see whether it can tell people with Alzheimer's disease from people with other forms of dementia -- and, more importantly, to see if it can tell whether or not a person with mild cognitive impairment is going to develop Alzheimer's disease.
That's O'Bryant's next step. His team already has patient blood samples and is ready to start testing them. All that's missing is the necessary funding.
Nixon, who was not involved in the O'Bryant study, hopes that funding comes soon for this and for other important areas of Alzheimer's research.
"It is incredibly important that we develop these biomarkers for early diagnosis and put in the necessary research to make this happen sooner rather than later," Nixon says. "We are falling behind in our need to address this Alzheimer's epidemic that is upon us right now. If we don't do it right now, we are going to suffer the consequences later."
O'Bryant and colleagues have filed for a patent on their Alzheimer's blood test, but declare no other relevant financial interests.
The findings are reported in the September issue of the Archives of Neurology.