Plasma Aβ42/40 ratio alone or combined with FDG-PET can accurately predict amyloid-PET positivity: a cross-sectional analysis from the AB255 Study Autor Virginia Pérez-Grijalba, Javier Arbizu, Judith Romero, Elena Prieto, Pedro Pesini, Leticia Sarasa, Fernando Guillen, Inmaculada Monleón, Itziar San-José, Pablo Martínez-Lage, Josep Munuera, Isabel Hernández, Mar Buendía, Oscar Sotolongo-Grau, Montserrat Alegret, Agustín Ruiz, Lluis Tárraga, Mercè Boada, Manuel Sarasa, The AB255 Study Group