At present there is no single test that leads to a diagnosis of AD. The doctor first needs to establish that the memory loss is abnormal and that the pattern of symptoms fits AD. This sometimes requires specialized memory testing. The doctor then needs to rule out other illnesses that can cause the same symptoms. For example, similar symptoms can be caused by depression, malnutrition, vitamin deficiency, thyroid and other metabolic disorders, infections, side effects of medications, drug and alcohol abuse or other conditions. If the symptoms are typical of AD and no other cause is found, the diagnosis is made. In the hands of a skilled doctor this diagnosis is very accurate.
An evaluation for Alzheimer's disease is often requested by a family member or friend who notices memory problems or unusual behavior. The doctor typically begins the evaluation by taking a health history and performing a physical examination, as well as evaluating the patient's cognitive abilities (mental processes of perception, memory, judgment, and reasoning).
This approach can help the doctor determine whether further testing is needed. A primary care physician may refer a patient for more extensive examination by a designated Alzheimer's diagnostic center, a neurologist, dementia or geriatric specialist. This examination will likely include a thorough medical evaluation and history, blood tests and brain scans (MRI or PET), followed by extensive neurological and neuropsychological assessments. A dementia evaluation should include interviews with family members or others who have close contact with the person being evaluated.
Rapid scientific progress is being made in identifying "biomarkers" of AD. Biomarkers are abnormal findings in blood, or cerebrospinal fluid (CSF), or on brain scans that are markers of AD. There is strong evidence that special tests of the CSF may be useful diagnostically. It is also possible now to see amyloid, a key abnormal protein in AD, in the brain using PET scans. As knowledge advances these tests may come into clinical use. Even now, however, it is clear that they will not be good enough to diagnose AD on their own. The diagnosis will still depend on a skilled and thorough evaluation.