There is currently no single test that can tell if a person has Alzheimer’s disease. The diagnosis is made through a systematic assessment which eliminates other possible causes.

Alzheimer’s disease is diagnosed when:

1. A person has sufficient cognitive decline to meet criteria for dementia
2. The clinical course is consistent with that of Alzheimer’s disease
3. No other brain diseases or other processes are better explanations for the dementia.

Alzheimer’s disease is diagnosed with the medical history and a physical examination. The physical examination is used to help find out if a physical problem may be causing a person’s dementia symptoms. It may be possible to correct some of these problems.

Diagnosis includes

Medical History
Questions are asked to the individual with Alzheimer’s disease and his/her family members or friends regarding the person’s symptoms now and in the past. The questions asked are regarding past diseases, family medical history, psychiatric history, etc.
Mental status exam
This process tests involves the person’s sense of time and place as well as the ability to remember, express himself/herself and perform simple calculations. It may involve exercises such as recalling words and objects, drawing and spelling, and simple questions like “Which month is it?”

Physical exam
To help rule out other causes, a physical exam will be done. The doctor will look for heart, lung, liver, kidney or thyroid problems that may be causing the symptoms. To evaluate whether other nervous system disorders are causing the symptoms, the doctor will test muscle tone and strength, co–ordination, eye movement, speech and sensation.

Laboratory tests
A number of tests will be done. Detailed blood test will be done to detect problems such as anemia, diabetes, thyroid problems or infections that might contribute to the symptoms.

Other tests such as X–rays and EEG’s (electroencephalogram) may be used to determine the source of the problem. In some centres, scans may be used. The following may be recommended, but are not always necessary for a diagnosis:

CT (computerized tomography) scan and MRI (magnetic resonance imaging) take images of the brain.

SPECT (single proton emission computed tomo–graphy) shows how blood is circulating to the brain.

PET (positive electron tomography) shows how the different areas of the brain respond during certain activities like reading and talking.

Psychiatric and psychological evaluations
A psychiatric evaluation may be helpful in ruling out other illnesses such as depression which can cause symptoms similar to Alzheimer’s disease. Neuro–psychological testing can evaluate memory, reasoning, writing, etc.

In addition, the person will undergo a mental and functional status examination and a mental health assessment. During these examinations, the person will be asked to perform simple tasks that check orientation.