For now, only an autopsy can prove the presence of Alzheimer's disease, but the clinical diagnosis is usually accurate. The current approach to establishing the cause of memory loss involves ruling out some potential causes and finding evidence to confirm the presence of others.
Once other conditions, such as depression, Huntington's disease, or hypothyroidism, have been ruled out, the diagnosis of Alzheimer's is made by accumulating information on the individual's history and mental status exams and by interviews with the patient, family members, and friends over a period of several weeks.
Diagnoses based on this type of clinical information are accurate about 90 percent of the time. According to the Diagnostic and Statistical Manual of Mental Disorders, a diagnosis of Alzheimer's disease requires the presence of memory impairment and at least one other cognitive deficit that is severe enough to affect social or job functioning (such as difficulty communicating). Also, the decline must be gradual.
Laboratory and imaging studies can provide information needed to diagnose many non-Alzheimer's dementias. Home-screening tests for Alzheimer's disease are available. However, we and the Alzheimer's Association advise against using them because of their inability to predict who does not have dementia and the potential for psychological distress.