Amyloid Beta 42 Peptide

This test may be used in patients with dementia. It helps tell Alzheimer's Disease apart from other forms of dementia.

Amyloid beta 42 peptide (Aß42) and Tau are two proteins associated with the development of neurofibrillary tangles (twisted protein fragments that clog nerve cells) and senile plaques (areas of dead nerve cells and protein deposits) that are found in the brains of patients with Alzheimer's Disease (AD). While the formation of neurofibrillary tangles and senile plaques is a normal part of aging, in people with AD they are present in greater numbers than in people without AD.

In a symptomatic patient, low Aß42 along with high Tau reflects an increased likelihood of Alzheimer's Disease, but it does not mean that the person definitely has AD. If a patient does not have abnormal levels of these proteins, then the dementia is more likely due to a cause other than AD.

The roles of Aß42 and Tau protein in the development of AD are not fully understood; however, this is an active area of research. The measurement of these two proteins in CSF is being evaluated for potential roles in diagnosis and monitoring of AD. Tests for Tau protein and Aß42 may be used as supplemental tests to help establish a diagnosis of Alzheimer's Disease.

If a patient has symptoms of dementia, such as memory loss, behavioral changes and decreased ability to perform daily life functions, the caregiver will do a thorough work-up to try to determine the cause. This work-up may include a variety of cognitive tests to assess memory and possibly scanning tests of the brain to look for abnormalities.


Cerebrospinal fluid (CSF) samples are collected using a lumbar puncture (spinal tap) procedure. This procedure is usually done in a hospital or clinic.


Greater than 450 units/L.

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.


Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.


It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.