There are no laboratory tests available that will positively diagnose Alzheimer disease (AD) during life. Currently, the only definite diagnosis of AD is to microscopically examine a section of the person's brain tissue after death. Pathologists look for senile plaques and neurofibrillary tangles characteristic of AD. Since plaque and tangle formation is also seen in normal aging, the sample must be compared to a control sample of normal, non-AD brain tissue from a person of the same age.
Health practitioners can make a reasonably accurate clinical diagnosis of AD by using a variety of tests and procedures to rule out other causes of dementia. When someone presents with symptoms of dementia, the health practitioner will evaluate the individual's personal and family history (preferably of several generations); perform a physical exam; determine the age of onset, and give the person neuropsychological tests to measure memory, language skills, and other cognitive functions.
The health practitioner may use a range of traditional laboratory tests to rule out deficiencies and other diseases and conditions that could be affecting the person's memory. The health care provider will also look for overmedication and may use imaging tools, such as computed tomography (CT) and magnetic resonance imaging (MRI) scans, to look for evidence of trauma, tumors, and stroke that could be causing dementia and to look for brain atrophy, shrinkage that may be present later in the Alzheimer disease progression.
If the health practitioner suspects AD, other less common laboratory tests (see Table) may be done to differentiate between AD and other forms of dementia and to check for genetic risk factors.
Tests to Aid in Categorization of Dementia
|Vitamin B12||Blood||B12 deficiency|
|Electrolytes||Blood||Na+, K+, Cl-, CO2 and pH balance|
|Drug screen||Urine||Illicit drug use|
Other Tests Used to Help Categorize Dementia
|Test Type||Test||Sample||Use||Associated With|
||CT (computed tomography)||Body scan||Rule out AD or with late stage AD||Stroke and brain atrophy (shrinkage associated with late stage AD)|
|MRI (magnetic resonance imaging)||Body scan||Rule out AD or with late stage AD||Stroke and brain atrophy|
|Less common lab tests||Amyloid Beta 42 peptide and Tau protein correlation (Tau/Aß42)||CSF||Used in research settings to establish presence of "tangles" or "plaque burden"; may help differentiate AD from other forms of dementia; Aβ42 used in some treatment trials||In symptomatic people, decreased Aß42 level along with an elevated Tau protein level indicates an increased likelihood of AD, regardless of the cause.|
|APOE genotype||Blood||Determine APOE genotype to provide risk factor assessment; adjunct test to confirm/rule out probable AD||Roughly 65% of AD patients have at least one APOE e4 allele; persons with 2 APOE e4 alleles have a much higher risk for AD, but this genotype is much less prevalent.|
|PSEN1||Blood||Test for genetic mutation||Associated with about half of the cases of early onset familial AD|
|PSEN2||Blood||Test for genetic mutation; available in only a few labs||Early onset familial AD; mutation very rare, identified in only a few family lines|
|APP||Blood||Test for genetic mutation; available in only a few labs||Early onset familial AD; mutation very rare, identified in only a few family lines|
Research is ongoing and new biomarkers, in addition to those listed in the table above, are being studied.