Plasma and CSF biomarkers in a memory clinic: Head‐to‐head comparison of phosphorylated tau immunoassays

Abstract Introduction Direct comparisons of the main blood phosphorylated tau immunoassays in memory clinic populations are needed to understand possible differences. Methods In the BIODEGMAR study, 197 participants presenting with cognitive complaints were classified into an Alzheimer's disease (AD) or a non‐AD cerebrospinal fluid (CSF) profile group, according to their amyloid beta 42/ phosphorylated tau (Aβ42/p‐tau) ratio. We performed a head‐to‐head comparison of nine plasma and nine CSF tau immunoassays and determined their accuracy to discriminate abnormal CSF Aβ42/p‐tau ratio. Results All studied plasma tau biomarkers were significantly higher in the AD CSF profile group compared to the non‐AD CSF profile group and significantly discriminated abnormal CSF Aβ42/p‐tau ratio. For plasma p‐tau biomarkers, the higher discrimination accuracy was shown by Janssen p‐tau217 ( r = 0.76; area under the curve [AUC] = 0.96), ADx p‐tau181 ( r = 0.73; AUC = 0.94), and Lilly p‐tau217 ( r = 0.73; AUC = 0.94). Discussion Several plasma p‐tau biomarkers can be used in a specialized memory clinic as a stand‐alone biomarker to detect biologically‐defined AD. Highlights Patients with an Alzheimer's disease cerebrospinal fluid (AD CSF) profile have higher plasma phosphorylated tau (p‐tau) levels than the non‐AD CSF profile group. All plasma p‐tau biomarkers significantly discriminate patients with an AD CSF profile from the non‐AD CSF profile group. Janssen p‐tau217, ADx p‐tau181, and Lilly p‐tau217 in plasma show the highest accuracy to detect biologically defined AD. Janssen p‐tau217, ADx p‐tau181, Lilly p‐tau217, Lilly p‐tau181, and UGot p‐tau231 in plasma show performances that are comparable to their CSF counterparts.