In the early stages, the symptoms of AD may be subtle and resemble signs that people mistakenly attribute to "natural aging." Symptoms often include:

• Repeating statements
• Misplacing items
• Having trouble finding names for familiar objects
• Getting lost on familiar routes
• Personality changes
• Losing interest in things previously enjoyed
• Difficulty performing tasks that take some thought, but used to come easily, like balancing a checkbook, playing complex games (such as bridge), and learning new information or routines

In a more advanced stage, symptoms are more obvious:

• Forgetting details about current events
• Forgetting events in your own life history, losing awareness of who you are
• Problems choosing proper clothing
• Hallucinations, arguments, striking out, and violent behavior
• Delusions, depression, agitation
• Difficulty performing basic tasks like preparing meals and driving

At end stages of AD, a person can no longer survive without assistance. Most people in this stage no longer:

• Understand language
• Recognize family members
• Perform basic activities of daily living such as eating, dressing, and bathing

The first step in diagnosing Alzheimer's disease is to establish that dementia is present. Then, the type of dementia should be clarified. A health care provider will take a history, do a physical exam (including a neurological exam), and perform a mental status examination.

Tests may be ordered to help determine if there is a treatable condition that could be causing dementia or contributing to the confusion of AD. These conditions include thyroid disease, vitamin deficiency, brain tumor, drug and medication intoxication, chronic infection, anemia, and severe depression.

AD usually has a characteristic pattern of symptoms and can be diagnosed by history and physical exam by an experienced clinician. Tests that are often done to evaluate or exclude other causes of dementia include computed tomography (CT), magnetic resonance imaging (MRI), and blood tests.

In the early stages of dementia, brain image scans may be normal. In later stages, an MRI may show a decrease in the size of the cortex of the brain or of the area of the brain responsible for memory (the hippocampus). While the scans do not confirm the diagnosis of AD, they do exclude other causes of dementia (such as stroke and tumor).