Engel, Brian

Abstract INTRODUCTION Determining apolipoprotein E ( APOE ) ε4 allele status, a key genetic risk factor for Alzheimer's disease (AD), requires molecular genotyping infrastructure not widely accessible beyond specialized centers. METHODS A fully automated high‐throughput apoE E4 proteotyping immunoassay was evaluated for clinical performance (460 participants across three cohorts) and analytical validity. Concordance with polymerase chain reaction (PCR)‐based genotyping and measures of analytical validity were reported. RESULTS The apoE E4 immunoassay demonstrated 99.6% (95% confidence interval [CI]: 98.4% to 99.9%) concordance with PCR‐based APOE ε4 genotype results across the pooled clinical cohort; 100.0% (95% CI: 97.1% to 100.0%) in those with AD ( N = 127) and 99.4% (95% CI: 97.8% to 99.8%) in those without AD (333). The assay met analytical validity criteria for E4 isoform specificity, interference, precision, and stability. DISCUSSION The apoE E4 immunoassay demonstrated high concordance with PCR‐based genotyping and robust analytical validity, offering an accessible alternative for APOE ε4 zygosity assessment. Highlights A novel high‐throughput plasma‐based proteotyping immunoassay for APOE ε4 zygosity classification was developed and evaluated for clinical performance and analytical validity. The apoE E4 immunoassay demonstrated high concordance (99.6%) with PCR‐based APOE ε4 genotyping across a diverse international cohort, and a robust analytical profile. An apoE E4 immunoassay may offer a more cost‐effective and accessible alternative to DNA genotyping approaches currently used for AD risk evaluation and anti‐amyloid treatment decisions.