There's no specific test today that confirms you have Alzheimer's disease. Your doctor will make a judgment about whether Alzheimer's is the most likely cause of your symptoms based on the information you provide and results of various tests that can help clarify the diagnosis.
Doctors can nearly always determine whether you have dementia, and they can often identify whether your dementia is due to Alzheimer's disease. Alzheimer's disease can be diagnosed with complete accuracy only after death, when microscopic examination of the brain reveals the characteristic plaques and tangles.
To help distinguish Alzheimer's disease from other causes of memory loss, doctors now typically rely on the following types of tests.
Physical and neurological exam
Your doctor will perform a physical exam, and is likely to check your overall neurological health by testing your:
- Muscle tone and strength
- Ability to get up from a chair and walk across the room
- Sense of sight and hearing
Blood tests may help your doctor rule out other potential causes of memory loss and confusion, such as thyroid disorders or vitamin deficiencies.
Mental status and neuropsychological testing
Your doctor may conduct a brief mental status test to assess your memory and other thinking skills. In addition, your doctor may suggest a more extensive assessment of your thinking and memory. Longer forms of neuropsychological testing may provide additional details about your mental function compared with others' of a similar age and education level.
Images of the brain are now used chiefly to pinpoint visible abnormalities related to conditions other than Alzheimer's disease — such as strokes, trauma or tumors — that may cause cognitive change. New imaging applications — currently used primarily in major medical centers or in clinical trials — may enable doctors to detect specific brain changes caused by Alzheimer's.
Brain-imaging technologies include:
- Magnetic resonance imaging (MRI). An MRI uses radio waves and a strong magnetic field to produce detailed images of your brain. MRIs are used to rule out other conditions that may account for or be adding to cognitive symptoms. In addition, they may be used to assess whether shrinkage in brain regions implicated in Alzheimer's disease has occurred.
- Computerized tomography (CT). A CT scan produces cross-sectional images (slices) of your brain. It's currently used chiefly to rule out tumors, strokes and head injuries.
Positron emission tomography (PET). During a PET scan, you'll be injected in a vein with a low-level radioactive tracer. The tracer may be a special form of glucose (sugar) that shows overall activity in various brain regions.
This can show which parts of your brain aren't functioning well. New PET techniques are able to detect your brain level of plaques (amyloid) and tangles (tau), the two hallmark abnormalities linked to Alzheimer's. However, these new PET techniques are generally found in research settings or in clinical trials.
- Cerebrospinal fluid. In special circumstances such as rapidly progressive dementia or very young onset dementia, a cerebrospinal fluid examination may be performed. The spinal fluid can be tested for biomarkers that indicate the likelihood of Alzheimer's disease.
Future diagnostic tests
Researchers are working with doctors to develop new diagnostic tools to help definitively diagnose Alzheimer's. Another important goal is to detect the disease before it causes the symptoms.
New tools under investigation include:
- Additional approaches to brain imaging
- More-sensitive tests of mental abilities
- Measurement of key proteins or protein patterns in blood or spinal fluid (biomarkers)
Genetic testing generally isn't recommended for a routine Alzheimer's disease evaluation. The exception is people who have a history of early-onset Alzheimer's disease. However, anyone with a family history of early Alzheimer's needs to meet with a genetic counselor to discuss the risks and benefits of genetic testing.