Plasma p217+tau versus NAV4694 amyloid and MK6240 tau PET across the Alzheimer's continuum

INTRODUCTION: We evaluated a new Simoa plasma assay for phosphorylated tau (P‐tau) at aa217 enhanced by additional p‐tau sites (p217+tau). METHODS: Plasma p217+tau levels were compared to (18)F‐NAV4694 amyloid beta (Aβ) positron emission tomography (PET) and (18)F‐MK6240 tau PET in 174 cognitively impaired (CI) and 223 cognitively unimpaired (CU) participants. RESULTS: Compared to Aβ− CU, the plasma levels of p217+tau increased 2‐fold in Aβ+ CU and 3.5‐fold in Aβ+ CI. In Aβ− the p217+tau levels did not differ significantly between CU and CI. P217+tau correlated with Aβ centiloids P = .67 (CI, P = .64; CU, P = .45) and tau SUVR(MT) P = .63 (CI, P = .69; CU, P = .34). Area under curve (AUC) for Alzheimer's disease (AD) dementia versus Aβ− CU was 0.94, for AD dementia versus other dementia was 0.93, for Aβ+ versus Aβ− PET was 0.89, and for tau+ versus tau− PET was 0.89. DISCUSSION: Plasma p217+tau levels elevate early in the AD continuum and correlate well with Aβ and tau PET.