There are no laboratory tests available that will positively diagnose Alzheimer's 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 the same age as the patient.
Doctors can make a reasonably accurate clinical diagnosis of AD by using a variety of tests and procedures to rule out other causes for dementia. When somone presents with symptoms of dementia, the doctor will evaluate his or her 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 his or her memory, language skills, and other cognitive functions. The doctor 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. They 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's Disease progression. If the doctor suspects AD, he or she may do other less common laboratory tests (see Table) 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 (shrinkage associated with late stage AD)|
|Less Common Lab Tests||Amyloid Beta 42 peptide and Tau protein correlation (Tau/Aß42)||CSF (cerebro-spinal fluid)||Help differentiate AD from other dementias||In symptomatic patients, 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 and adjunct test to confirm/rule out probable AD||ApoE e4 associated with increased risk of late onset AD in symptomatic patients; e4 and e2 variations also associated with lipid disorders|
|PSEN1||Blood||Test for genetic mutation||Thought to cause about half of the cases of Early Onset Familial AD|
|PSEN2||Blood, available in only a few labs||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; still in research - not clinically available||Early Onset Familial AD; mutation very rare, identified in only a few family lines|