Performance of a fully automated plasma tau phosphorylated at threonine 217 immunoassay to reflect amyloid-beta burden in an unselected cohort representative of clinical practice

Background: With the emergence of disease-modifying anti-amyloid-beta (Aβ) therapies for Alzheimer's disease (AD), early and accurate quantitative measures of Aβ burden are critical. Blood-based biomarkers are a scalable and minimally invasive diagnostic solution; plasma tau phosphorylated at threonine 217 (pTau217) is a promising marker for Aβ pathology. The clinical performance of the prototype ElecsysⓇ Phospho-Tau (217P) Plasma immunoassay (Roche Diagnostics) to detect Aβ burden was investigated in an unselected cohort reflective of clinical practice.

Methods: Plasma was prospectively collected from participants aged 55 to 80 years with objective or subjective cognitive decline under evaluation for AD. Participants were recruited at multiple clinical sites spanning primary and secondary care. Plasma pTau217 concentrations measured using the prototype pTau217 plasma immunoassay were compared with amyloid positron emission tomography centiloid-based classification at different cutoffs, with further analyses performed at centiloid cutoff 30.

Outcomes: Among 588 participants, plasma pTau217 demonstrated high concordance with centiloid-based classification at selected cutoffs. The discriminative ability of plasma pTau217 to detect Aβ pathology peaked at centiloid cutoff 32 (area under the curve=0.933). Subgroup analyses at centiloid cutoff 30 demonstrated good discrimination of Aβ positivity/negativity by clinical diagnosis, age, and sex. Moderately decreased kidney function to kidney failure was found to influence plasma pTau217 levels.

Interpretation: The prototype pTau217 plasma immunoassay showed high accuracy in reflecting Aβ burden among individuals presenting with cognitive complaints across diverse clinical settings. These findings support its potential implementation into routine clinical practice for early detection of AD, alongside standard clinical and neuropsychologic assessments.