How do doctors diagnose Alzheimer's disease?
Since there are multiple possible causes of dementia, Alzheimer's often becomes a diagnosis of exclusion. Certain factors point to it as a cause of mental decline.
Patient History
Physical examination
Cognitive assessment tests
Biomarkers
Brain Imaging
Patient History
Persons with Alzheimer's disease, or more often their caregivers, will describe a pattern of loss of recent and remote memory, as well as a decline in abstract thinking abilities and poor judgment. Consciousness is normal in the first stages. It is imperative that the physician rule out other organic causes of dementia, such as vitamin B12 deficiency or depression, that might be mistaken for Alzheimer's disease.
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Physical examination
A complete physical examination with a thorough evaluation of blood tests must be performed.  Those blood tests include a complete blood count, blood chemistry tests, thyroid function studies, folate and vitamin B12 levels, syphilis test, and urinalysis. Other tests such as electrocardiogram and various X-rays can be ordered at the discretion of the physician.
CT scans or MRIs of the brain can be done to evaluate for other conditions that may contribute to memory loss, including stroke, bleeding around the brain, a brain tumor, or a condition called normal pressure hydrocephalus (an excess of brain fluids).
While a special blood test can be ordered to look for the presence of apolipoprotein E4, the gene that increases the risk of Alzheimer's disease, most doctors do not feel this test has any diagnostic value as even people without the ApoE4 gene can develop Alzheimer's disease.
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Cognitive assessment tests
A variety of tests exist that can measure different thinking abilities, including memory and language function. These include the Mini Mental Status Exam, the Blessed Dementia Scale, the Short Portable Mental Status Questionnaire, and the Mattis Dementia Rating Scale, among others. The Mini Mental Status Exam, for example, includes such questions as "What is the date?" and "Where are we now?" It asks the patient to perform some mathematical calculations, to follow three-step directions, to read and follow a command, and to reproduce a figure drawn on paper. Each exercise has a value of 1, 3, or 5 points, with a perfect score being 30. Any score under 23 raises concerns about dementia, but this value varies based on a person's age and education level.
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Biomarkers
Scientists are working on ways to diagnose Alzheimer's disease more quickly and accurately. Kits to test for the beta-amyloid and tau proteins in the cerebrospinal fluid are available, and recent research shows they are quite accurate at diagnosing Alzheimer's. Currently, these tests are not widely used in clinical practice, however. Tests to measure substances associated with free radical damage in urine are in development, and experimental results show they may be able to detect Alzheimer's disease with a high degree of accuracy as well.
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Brain Imaging
Technology for imaging the brain is continually improving. Alzheimer's researchers are particularly interested in a technology called functional magnetic resonance imaging (fMRI), which may allow them to diagnose Alzheimer's by pinpointing dysfunctional areas of the hippocampus, the brain's memory center; structural, or regular MRI, which may aid in diagnosis by measuring overall brain shrinkage; and positron emission topography (PET), which in combination with radioactive markers may allow scientists to image the plaques and tangles of Alzheimer's disease in living patients.
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