There is no single, comprehensive diagnostic test for Alzheimer's disease. A differential diagnosis requires a complete medical, neurological and psychiatric evaluation, neuropsychological tests, as well as a complete history from the patient's family, including a description of the symptoms and progression. Whether or not the patient has Alzheimer's can only be determined by careful examination.

The diagnostic process may be handled by a family physician or may involve a diagnostic team of medical professionals, including the primary physician, neurologist (a physician specializing in the nervous system), psychiatrist, psychologist and nurses. The diagnostic process generally takes more than one day and is usually performed on an outpatient basis. It may involve going to several different locations or even to a specialized Alzheimer diagnostic center. It is very important that someone who can describe recent behavioral changes as well as past history accompany the patient to the work-up.

Once the tests are completed, a diagnosis of "probable" Alzheimer's disease can be made by process of elimination. However, physicians can only be 80 to 90 percent certain their diagnosis is accurate. Unfortunately there is no known way to detect the abnormal structures in the brain of a living person, and a definitive diagnosis of Alzheimer's cannot be made except through autopsy.