Not yet in routine medical practice. Recently, Alzheimer's tests have been developed that can identify biomarkersknown to be linked to the later development of dementia symptoms due to Alzheimer's disease. Because of this, in April 2011, a panel of experts recommended new criteria for diagnosing and defining Alzheimer's disease. Whereas the previous criteria (from 1984) required the presence of dementia symptoms in order to diagnose Alzheimer's disease, experts now believe that Alzheimer's disease involves a gradual progression through three main phases. These are: a preclinical phase with biomarkers but no symptoms; a middle phase of mild cognitive impairment during which some symptoms are detectable but the person can still function independently, and then a fully symptomatic phase of Alzheimer's dementia.
The new biomarker tests aren't yet standardized or widely available, however. Mostly they're now used to help identify and sort research subjects. Also, there's much that scientists don't yet understand about what these biomarkers mean over the longer term. For example, the presence of biomarkers doesn't reveal when actual disease symptoms might appear. It's also unclear whether all people who have biomarkers will even go on to develop symptoms. Adding another wrinkle: Dementia symptoms can be brought on by causes other than Alzheimer's, such as a brain tumor, medication side effects, or strokes. So a test may tell you that you're free of Alzheimer's biomarkers, but you could develop dementia of another stripe anyway.
A rare near-exception to foretelling Alzheimer's disease in someone who's having no symptoms is someone with a strong family history of early onset (before age 60, also called young-onset) Alzheimer's. Certain genes have been identified that are strongly associated with this form of the disease. For this unique subset of people, genetic testing can indicate one's likelihood of developing early onset Alzheimer's. However, only about 1 percent of all cases of Alzheimer's dementia are this familial early onset type.