There are no laboratory tests available yet that will definitively diagnose Alzheimer’s Disease. If a patient has symptoms of dementia, such as memory loss, behavioral changes, and decreased ability to perform daily life functions, their doctor will do a thorough work-up to try to determine the cause. Cerebrospinal fluid levels of Tau protein and Aß42 are measured in patients with symptoms of dementia. They are used along with other tests and procedures to help differentiate between AD and other causes of dementia, such as vascular dementia (involving strokes and tumors), overmedication, and thyroid disease.

Tau protein and Aß42 assessments are done when a patient has symptoms of dementia and their doctor is trying to differentiate between AD and other forms of dementia. It may be done in conjunction with other laboratory testing (such as ApoE genetic testing), with imaging scans like an MRI (magnetic resonance imaging - done to look for brain abnormalities, strokes, and tumors), with a thorough medical and neuropsychological evaluation, and with an examination of a patient’s family history to determine the likelihood of AD.

As Aß42 accumulates in the brain, its level decreases significantly in the cerebrospinal fluid. In a symptomatic patient, a decreased Aß42 level along with an elevated Tau protein level indicates an increased likelihood of Alzheimer’s Disease, but it does not mean that the person definitely has AD. If a patient does not have a decreased Aß42 but has an elevated Tau level, then their dementia is more likely due to a cause other than AD.

PLEASE NOTE: Numerically reported test results are interpreted according to the test's reference range, which may vary by the patient's age, sex, as well as the instrumentation or kit used to perform the test. A specific result within the reference (normal) range – for any test – does not ensure health just as a result outside the reference range may not indicate disease. To learn more about reference ranges, please see the article, Reference Ranges and What They Mean. To learn the reference range for your test, consult your doctor or laboratorian. Lab Tests Online recommends you consult your physician to discuss your test results as a part of a complete medical examination.

Assessments of Aß42 and Tau protein levels should ONLY be done on patients with symptoms of dementia. They do not establish a diagnosis of Alzheimer’s Disease; they are only an indicator that should be used in conjunction with other tests and the patient’s clinical and family history.

In patients with probable AD, studies have shown that the correlation between decreased Aß42 levels and elevated Tau protein levels holds true regardless of the cause or the age of onset of Alzheimer’s Disease.

Looking at the correlation between Tau protein and Aß42 levels is still a fairly new test. It has not yet gained wide acceptance and is only available in a few laboratories. Your doctor may or may not recommend this testing. If they do, your cerebrospinal fluid samples will need to be sent to a reference laboratory and the results may take several days to return.