Elecsys pT181p immunoassay: Clinical performance for ruling out amyloid pathology.

INTRODUCTION

Plasma biomarker rule-out tests can be used early in the Alzheimer's disease (AD) diagnostic pathway to identify people with low likelihood of amyloid pathology.

METHODS

A care setting-agnostic cutoff for the Elecsys® Phospho-Tau (181P) plasma (pT181p) immunoassay was determined and validated in two independent, diverse cohorts, representative of real-world clinical practice (N = 604; N = 787, respectively). An additional cutoff was assessed in a subset of people reflective of primary care (n = 312).

RESULTS

At a care setting-agnostic cutoff of 0.934 pg/ml, high negative predictive value (NPV) (93.8%) and acceptable positive predictive value (PPV) (46.6%) were observed against amyloid-positron emission tomography (PET). A primary care-specific cutoff of 0.722 pg/ml showed high NPV (97.9%) against amyloid-PET. Amyloid positivity prevalence for each cutoff population was 22.5% and 13.1%, respectively.

DISCUSSION: The pT181p immunoassay is a high-performance test that may substantially help improve access to amyloid pathology testing for people requiring confirmation, potentially leading to timely clinical decisions and better outcomes.