CSF tau levels are measured before surgery and 24 hours and 6 weeks after surgery at the Alzheimer’s Disease Neuroimaging Initiative biomarker core lab that has well-validated multiplex ELISA-based bead assays for CSF tau, phospho-tau, and amyloid-beta levels.To avoid measurement bias, sample measurements are performed in random order, and technicians are blinded to study subject number and time point. To minimize confounding fromdiurnal variation, CSF samples per patient are collected atthe same time of day ( 1 h) whenever possible.