How is Alzheimer's disease diagnosed?

Clinicians diagnose "probable" Alzheimer's disease by doing a thorough diagnostic workup. This can include a complete medical history; physical examination to find evidence of any underlying medical or neurological disorders that may be contributing to symptoms; neuropsychological tests that gauge memory, attention, language skills, and problem-solving abilities; laboratory tests that can include blood and urine samples; and brain imaging scans, such as a CT scan, MRI, SPECT, or PET scan, which can identify changes in brain structure or activity.

For Medicare beneficiaries, a new annual wellness visit (AWV) includes “detection of any cognitive impairment” as well as personalized prevention plan services. A health provider will assess cognitive impairment by direct observation and consideration of information obtained from patient reports and concerns raised by family members, friends, caregivers, or others. This provision, part of the new healthcare reform law, took effect January 1, 2011.

A beneficiary is entitled to an AWV by a primary care provider or other health provider after having Medicare Part B coverage for at least 12 months and not having had an AWV or the “Welcome to Medicare Visit” initial preventative physical exam within the past 12 months. There is no coinsurance or deductibles for the AWV.

The causes of dementia are complex; a complete clinical evaluation by a skilled clinician will identify the primary cause of dementia in more than 90% of cases. Clinicians diagnose Alzheimer’s disease as the cause of dementia in about 60% of individuals living with the disease.

Alzheimer's disease is characterized by two types of abnormal lesions in the brain: Beta-amyloid plaques, sticky clumps of protein fragments and cellular material that form outside and around neurons, and neurofibrillary tangles, insoluble twisted fibers composed largely of the protein tau that build up inside nerve cells. Although these structures are hallmarks of the disease, scientists are still unclear whether they cause it or are a by-product of it.
Dr. Eric Pfeiffer
Psychiatrist (Therapist)
Only a doctor, preferably one who is a specialist in memory disorders can make a definite diagnosis of Alzheimer’s disease. In order to do so the doctor will need all of the following items:
  • a detailed history of how memory problems have developed, obtained from both the patient and the caregiver
  • a thorough general medical history
  • a complete physical and neurological examination
  • a battery of lab tests to include a complete blood count, tests of liver and kidney function, cholesterol and other lipid tests and a fasting blood sugar
  • a standard cardiogram (EKG)
  • at least one imaging study of the brain, preferably an MRI scan of the brain, or a CAT scan, or even better, a PET scan of the brain
  • an assessment of the degree of memory deficit, using one of the memory screening instruments: the Mini-Mental Stratus Examination (Folstein MMSE) or the Short Portable Mental Status Questionnaire (Pfeiffer SPMSQ)
  • in selective cases, a full-scale neuropsychological evaluation by a psychologist
  • still more selectively, certain genetic tests, and measurement of A beta 42 amyloid and tau protein, in cerebrospinal fluid, blood or urine
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Cardiologist (Heart Specialist)
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The only certain diagnosis for Alzheimer's disease cannot be done until after death, when evidence of plaques, tangles and shrinkage of the brain can be seen.

For living patients, doctors may test various bodily fluids, such as urine, blood and spinal fluid.

A doctor might also use a brain scan, such as MRI, PET or CT scan, to look for unusual formations in the brain.

An interview also can provide useful information about memory and other health issues. Some simple tests can also help find out more about the patient's attention span, counting abilities and short-term and long-term memory.

Most importantly, a doctor needs to rule out other potential causes for the patient's problems, such as other forms of dementia, cognitive impairments, minor strokes or other conditions that can produce symptoms similar to Alzheimer's.

Judith London, MD
Psychiatrist (Therapist)

Another problem in diagnosing Alzheimer's is that often there is more than one cause for the series of symptoms characteristic of dementia. Once the brain is compromised with something such as a small or major stroke, previous head injury, or oxygen interruption, the brain may be vulnerable to Alzheimer's, just as people with Alzheimer's may be more vulnerable to another brain condition that causes dementia.

In those cases, there is a mixed dementia that confounds a clear-cut diagnosis.

A healthcare provider will likely use a variety of methods to arrive at a diagnosis of Alzheimer's disease (AD). These diagnostic tools also help rule out other forms of dementia or health conditions that may produce dementia-like symptoms, such as alcohol abuse, blood vessel diseases, brain tumors, infections, medication interactions or side effects, mood disorders, neurological problems, thyroid disorders, or nutritional deficiencies.

Doctors may use the following diagnostic tools:

  • Evaluation of Symptoms. Healthcare providers rely on the patient and the patient's loved ones to provide a full description of symptoms, including what the patient is experiencing, when his or her symptoms began, and how frequently the symptoms occur.
  • Medical History. Full disclosure of a patient's past and current medical conditions and procedures, surgeries, and traumas, as well as a complete list of his or her medications, vitamins, herbs, and supplements is necessary to help narrow a diagnosis. Information about diet, lifestyle, and family history of disease also is important.
  • Physical Exam. A physical exam may include evaluation of the heart, lungs, and blood pressure. The neurological component of the exam will assess reflexes, coordination, muscle function, speech, physical sensation, and eye movement.
  • Psychological/Psychiatric Exam. Evaluation of emotional or mental conditions can help determine if an underlying mood disorder such as depression may contribute to symptoms.
  • Lab Tests. A healthcare provider may test samples of blood, urine, or spinal fluid to help rule out other conditions that may be responsible for symptoms.
  • Brain Scans. An MRI, CT scan, PET scan or other form of imaging helps healthcare providers detect any brain abnormalities that may indicate AD or other disorders.
  • Neuropsychological Tests or Mental Status Exam. These tests detect and assess impairments in memory, language, comprehension, and reasoning skills.
Dr. Zaldy S. Tan, MD
Geriatric Medicine Specialist

Doctors use a variety of methods and tests to diagnose Alzheimer’s disease. They gather information through:

  • Medical and family history
  • Neurological tests, including memory and language tests
  • Psychological tests
  • Blood tests
  • Radiology tests, including a computed tomography (CT) scan and magnetic resonance imaging (MRI)

Part of diagnosing Alzheimer’s is ruling out other conditions that may cause memory loss. Once the evaluation is complete, a memory expert can evaluate the results and make a diagnosis. Although many patients view a memory evaluation as stressful, it does not have to be if you know what to expect. Familiarize yourself with the evaluation process to make the visit less daunting.

Alzheimer's disease is a clinical diagnosis. There are several types of dementia (disorder in memory). Alzheimer's for the most part is the diagnosis when other forms of dementia have been ruled out. There is a genetic test that can diagnose about 4 percent of the cases of dementia, but the majority of Alzheimer's patients do not have that gene.
Primary care doctors as well as neurologists, psychiatrists and geriatricians typically diagnose and treat Alzheimer's disease. An evaluation usually requires two or more visits of 30 minutes or more, plus testing. The diagnostic process includes a thorough medical history and family interview, including questions about your current mental and physical conditions with an emphasis on any noticeable physical, mental and emotional changes. The doctor will want to get information from someone who knows you well, since you may not recognize your own limitations or symptoms. A healthcare professional should also ask for a list of prescription drugs and take a family health history. Routine tests, such as blood work, blood pressure screening and urine tests, will be part of a comprehensive physical evaluation.

Alzheimer's patients have characteristic changes in the brain, but there is no single, comprehensive test for diagnosing the disease. Doctors diagnose Alzheimer's by ruling out other conditions through a process of elimination. The only way to confirm a diagnosis of Alzheimer's disease is through autopsy.

When Alzheimer's disease is detected in its early stages, treatment can begin earlier and its effectiveness is increased as most medications currently available or in development can only slow the patient's descent into forgetfulness. Doctors at NewYork-Presbyterian are using a new brain imaging technique called quantitative diffusion tensor imagery to distinguish Alzheimer's from treatable disorders with similar symptoms such as normal pressure hydrocephaly. Doctors here also conduct genetic testing for the disease in people with a family history of Alzheimer's.

Dr. Gary Small, MD
Psychiatrist (Therapist)

Several steps are involved in diagnosing Alzheimer’s disease. 

The first step is a comprehensive history. Because the person has a memory problem and won’t remember all the details, the doctor will talk to the person’s caregivers. The doctor wants to know how quickly the symptoms started and if the person has any other health conditions that might raise their risk for cognitive impairment. 

Exams and tests to diagnose Alzheimer’s include: 

  • Physical exam
  • Neurological exam
  • Mental status exam, using standardized tests such as the Mini-Mental State Exam (MMSE) or the Hamilton Depression (HAMD-D) scale to make sure depression isn’t the cause of the symptoms
  • Functional assessment to determine independence
  • Laboratory tests to check for anemia and problems with thyroid or metabolism 
  • Computerized tomography (CT) or magnetic resonance imaging (MRI) brain scan to check for a tumor, stroke or illness that could be reversible

Sometimes, doctors also order a positron emission tomography (PET) scan to rule in Alzheimer's disease or frontotemporal dementia, which can have implications for the treatment.

The first step in diagnosing Alzheimer's disease initially is to exclude some mimics of the disease, or conditions that can present with forgetfulness. For example, there are conditions where forgetfulness could indicate a mood disorder, such as depression.

Some nutrition abnormalities or endocrine abnormalities would also need to be excluded because they can present with some cognitive complaints. If all of these factors are excluded, the next step would be to do a more thorough cognitive evaluation. Frequently that starts with an in-office cognitive test. Sometimes that lacks sensitivity, so a neuropsychological evaluation, which is an objective memory and cognition evaluation, would be done.

If the diagnosis is still in doubt more specific testing would follow, such as evaluating how the brain is functioning. Doctors would evaluate how the brain is using glucose and whether there are any areas of the brain that have decreased usage of glucose, which would point to a certain pathology or more specific biomarker studies.

Doctors can also perform a lumbar puncture, also known as spinal tap, to check for the specific changes that would be seen with Alzheimer's disease.

Trinity Health is a Catholic health care organization that acts in accordance with the Catholic tradition and does not condone or support all practices covered in this site. In case of emergency call 911. This site is educational and not a substitute for professional medical advice, always seek the advice of a qualified health care provider.

Alzheimer's disease can only be diagnosed with complete certainty after death using an autopsy. However, by questioning those affected and their family members, combined with using lab tests and brain scans, doctors are able to accurately diagnose Alzheimer's nine out of ten times. Using questions to determine someone's level of brain function can be very effective, as well as talking to family members about the symptoms being displayed.

Alzheimer's is difficult to diagnose because there are several causes of dementia, but blood tests can be used to narrow down the possible causes. Similarly, brain scans like magnetic resonance imaging (MRI) and computerized tomography (CT) can be used to look for visual clues.

Dr. Christine Ganzer
Geriatrics Nursing Specialist

A definitive diagnosis can only be achieved by conducting a biopsy of the brain but doctors can with good certainty determine whether or not the patient is suffering from Alzheimer’s through the use of tests.

Alzheimer's disease is diagnosed upon the exclusion of other neurodegenerative disease processes that may cause cognitive impairment or memory changes. The best way to be certain that the diagnosis is Alzheimer’s is to have some simple but specific tests that can be ordered by a qualified clinician that practices in the area of dementia. Typically these tests include neuropsychological testing that can localize areas of the brain where the deficits are occurring thereby helping the clinician identify other disease processes, blood tests that can eliminate deficiencies that can contribute to cognitive changes and Neuroimaging studies such as Positron Emission Tomography (PET) which can reveal abnormal cellular activity in the brain. Currently there are no cures for Alzheimer’s disease but there are medications such as Donepezil (Aricept), Rivastigmine (Exelon) and Memantine (Namenda) that have had some success in slowing down the disease process.


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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.