False positive plasma p‐tau217 results associated with heterophilic antibody interference: A potential clinical pitfall

INTRODUCTION: Plasma phosphorylated tau at threonine 217 (p-tau217) has emerged as one of the most promising blood-based biomarkers for Alzheimer's disease (AD). While rare, heterophilic antibodies (HAb) are a persistent potential confounding factor in immunoassays. METHODS: Potential HAb interference in the Lumipulse G pTau217 assay in samples exhibiting concentrations > 10 pg/mL were investigated. Samples were subjected to HAb blocking reagent (HBT), and in some cases, polyethylene glycol (PEG) precipitation and serial dilutions. RESULTS: In 14 of the 15 suspected HAb cases, HBT treatment greatly reduced measured p-tau217 concentrations. and in one of three specimens selected for further investigation, reduced Aβ42 concentrations PEG precipitation in the three selected samples also reduced p-tau217 concentrations, while serial dilution yielded mixed effects. Control specimens were unaffected by sample treatment or dilutions. DISCUSSION: HAb may result in falsely elevated p-tau217 and p-tau217/Aβ42 ratio. HAb interference should be considered in cases of unusually high p-tau217 concentrations prior to clinical interpretation. HIGHLIGHTS: Potential heterophile antibody (HAb) interference in the Lumipulse p-tau217 immunoassay was investigated. Investigation was performed using HAb blocking reagent, and in some cases also using PEG precipitation . Patients with p-tau217 concentrations > 10 pg/mL exhibited positive HAb interference in 14 of 15 cases. HAb interference can lead to falsely positive p-tau217/Aβ42 ratios.