A new test that finds irregular patterns in a patient's blood could help doctors predict Alzheimer's two to six years before its onset. In this breakthrough study, researchers in the United States and Europe conducted two tests on people who ranged from having no symptoms to having full dementia. The first test successfully matched people's diagnoses 90 percent of the time. In the second test, blood samples predicted with 91 percent accuracy whether someone would develop Alzheimer's. While the blood test won't be available for several years, this new knowledge brings us closer to understanding the complexities of this disease.