Determination of the amyloid tau index. CSF concentrations of Aβ1-42, total tau (T-tau) and phosphorylated tau (P-tau181) were measured using commercially available enzyme-linked immunosorbent assays (ELISA INNOTEST p-tau-181, INNOTEST htau, INNOTEST β-amyloid (1-42) kits; Innogenetics, Gent, Belgium) according to manufacturer's instructions..