Cerebrospinal fluid AΒ42, total tau, and phosphorylated tau in the evaluation of Alzheimer’s dementia: Experience from a commercial reference laboratory

Background Aβ amyloid plaques and tau neurofibrillary tangles play an important role in Alzheimer’s disease (AD) pathophysiology, and the CSF biomarkers Aβ42, total tau (T‐tau), and phosphorylated tau181 (P‐tau) have been extensively used in diagnosing AD. Here we describe our experience with use of the Aβ42/T‐tau index (ATI) and P‐tau for classification of patients with suspected AD. Method A convenience sample of results from CSF specimens submitted to a commercial reference laboratory for measurement of Aβ42, T‐tau, and P‐tau (presumably for diagnosis in patients with suspected AD) was selected for analysis. Each marker was measured using sandwich ELISA−based tests. The ATI was calculated as Aβ42/(240 + (1.18 × T‐tau)). AD classification was based a combination of ATI and P‐tau thresholds: not consistent with AD (not‐AD; P‐tau 1.2); borderline (P‐tau 54‐68 pg/mL and/or ATI 0.8‐1.2); AD (P‐tau >68 pg/mL or ATI