Mielke MM, et al. - Authors compared the plasma phospho-tau181 (pTau181) and total tau: (1) across the Alzheimer's disease (AD) clinical spectrum; (2) in association with brain amyloid β (Aβ) positron emission tomography (PET), tau PET, and cortical thickness; and (3) as a screening tool for elevated brain Aβ. These were observed across cognitively unimpaired, mild cognitively impaired, and AD dementia patients. In contrast with the cognitively unimpaired patients, the plasma total tau and pTau181 levels were found to be higher in AD dementia patients. Plasma pTau181 illustrated a stronger relation with both Aβ and tau PET. Thus, plasma pTau181 exhibited the potential as a biomarker of AD pathophysiology and as a noninvasive screener for elevated brain Aβ.