Beta-Amyloid is a peptide of 39-43 amino acids that is derived from Amyloid Precursor Protein (APP). In a healthy brain, beta-amyloid is broken down and eliminated, while in Alzheimers disease (AD), the fragments accumulate to form hard, insoluble plaques (senile plaques). This test plays a role in the diagnosis and monitoring of AD. In addition to AD, amyloid plaques formation also appears in some variants of Lewy body dementia, inclusion body myositis, and cerebral amyloid angiopathy. INCREASED amyloid plaque formation therefore reflects an increased likelihood of Alzheimers disease.