CSF biomarkers of Alzheimer's disease concord with amyloid‐β PET and predict clinical progression: A study of fully automated immunoassays in BioFINDER and ADNI cohorts

Abstract Introduction We studied whether fully automated Elecsys cerebrospinal fluid (CSF) immunoassay results were concordant with positron emission tomography (PET) and predicted clinical progression, even with cutoffs established in an independent cohort. Methods Cutoffs for Elecsys amyloid‐β 1–42 (Aβ), total tau/Aβ(1–42), and phosphorylated tau/Aβ(1–42) were defined against 18 Fflutemetamol PET in Swedish BioFINDER (n = 277) and validated against 18 Fflorbetapir PET in Alzheimer's Disease Neuroimaging Initiative (n = 646). Clinical progression in patients with mild cognitive impairment (n = 619) was studied. Results CSF total tau/Aβ(1–42) and phosphorylated tau/Aβ(1–42) ratios were highly concordant with PET classification in BioFINDER (overall percent agreement: 90%; area under the curve: 94%). The CSF biomarker statuses established by predefined cutoffs were highly concordant with PET classification in Alzheimer's Disease Neuroimaging Initiative (overall percent agreement: 89%–90%; area under the curves: 96%) and predicted greater 2‐year clinical decline in patients with mild cognitive impairment. Strikingly, tau/Aβ ratios were as accurate as semiquantitative PET image assessment in predicting visual read–based outcomes. Discussion Elecsys CSF biomarker assays may provide reliable alternatives to PET in Alzheimer's disease diagnosis.