Determining whether or not someone has Alzheimer's disease (AD) is not an exact science, but there are several tests that can help ensure an accurate diagnosis. These include brain imaging, genetic testing, and neuropsychological testing. The tests can also help rule out other possible conditions and diseases.
MRI (Magnetic Resonance Imaging)
An MRI takes multiple images of the brain using powerful magnets and radio waves. It can help detect:
- developmental and structural abnormalities
- inflammatory conditions
- problems with the blood vessels
It’s a pain-free, noninvasive procedure, and takes more than an hour. You lie down on a table that slides into the MRI machine. You may have a contrast dye injected into your arm to enhance the images. You will have to remove all metallic objects, like jewelry, eyeglasses, and hair clips. In terms of preparation, you may be asked not to eat or drink anything (fast) for four to six hours before the MRI.
Be sure to let the doctor know ahead of time if you are uncomfortable in small spaces. They can prescribe medication to help you relax, or recommend an "open" MRI. An open MRI is less visually confining than the standard MRI machine. People with cardiac pacemakers typically cannot have an MRI and should not enter an MRI area. If you have a cardiac pacemaker, make sure you tell your doctor, and you will be advised on your particular circumstances. You may not be able to have an MRI if you have any of the following metallic objects in your body:
- brain aneurysm clips
- certain types of artificial heart valves
- heart defibrillator or pacemaker
- inner ear (cochlear) implants
- recently placed artificial joints
- certain types of vascular stents
CT (Computed Tomography) Scan
A CT scan uses x-ray technology to create multiple images of the brain. It helps detect conditions like:
- bleeding in the brain
- skull fractures
- blood clots
- brain tumors
- enlarged brain cavities
- other signs of brain disease
A CT scan is a pain-free and noninvasive test that last a few minutes. Like the MRI, you will lie down on a table that slides into the CT machine. You have to lie still during the procedure and may have to hold your breath for short periods of time. You may be asked to wear a hospital gown and to remove all metal objects. You may have a contrast dye injected into your arm to enhance the images. In terms of preparation, you may be asked to fast for four to six hours beforehand.
PET (Positron Emission Tomography) Scan
A positive emission tomography ( PET) scan is an imaging test that can provide information on how the brain and its tissues function on a cellular level. It's used to detect changes in glucose metabolism, oxygen metabolism, and blood flow, all of which can reveal abnormalities of brain function.
Like the MRI and CT scan, you will need to lie down on a table that slides into the PET scan machine. About an hour prior to the PET scan, a small amount of radioactive material (a tracer) is injected into a vein in your arm, or you will inhale it. You may be asked to perform various mental tasks, like reading or naming letters. This diagnostic tool allows the doctor to see levels of brain activity. Being required to fast for four to six hours prior to the test is not unusual. This test usually takes between 30 minutes and two hours.
According to the Alzheimer’s Association, research studies have shown that amyloid plaque buildup can be detected with PET scan technology, even before symptoms are evident. It's still unknown if these plaques are risk factors for AD, the result of the disease, or some combination thereof. Using PET scans as an early detection diagnostic tool is still being developed and isn't ready for use by general practice clinicians. If you have diabetes, be sure to share that information with your doctor. Blood sugar or insulin levels may affect the PET scan test results.
Researchers now know of 10 genes believed to be associated with AD. The most notable is the gene apolipoprotein E (APOE). While genetic blood tests are available, they don’t provide a definitive diagnosis. Additionally, having "AD genes" only increases your risk of developing AD — it doesn't mean you have it. There are people with the "AD genes" who never develop AD.
Studies of families with a history of early-onset AD have identified defects in three different genes. They are APP (on chromosome 21), PSEN-1 (on chromosome 14) and PSEN-2 (on chromosome 1). People with mutations on one or more of these genes tend to develop early-onset AD. All of these can be detected with a specialized genetic blood test. There are people who suffer from early-onset AD who don't have mutations in any of these genes.
Additionally, prenatal diagnosis using amniocentesis during pregnancies can detect an increased risk for the PSEN1 mutation. However, this test is unlikely to be performed unless a family member has been diagnosed with the genetic mutation. The presence of a mutation does not guarantee an individual will develop Alzheimer's disease.
The most commonly used neuropsychological test is the mini-mental state exam (MMSE). During the MMSE, you are asked questions and given instructions designed to evaluate your basic mental status. You may be asked the day's date and the date of your birthday. You may also be asked to repeat a list of words or phrases and to count backwards from 100 by sevens. No advanced preparation is needed for this test.