Rapid Apolipoprotein E ε4 Proteotyping for Alzheimer’s Disease Anti-Amyloid Therapy Eligibility and Risk Assessment

Background: Anti-amyloid therapies for Alzheimer’s disease (AD) are associated with amyloid-related imaging abnormalities (ARIA), with apolipoprotein E ε4 ( APOE4 ) homozygosity conferring the highest risk. Given the new clinical need, novel plasma proteotyping assays may offer a rapid and high-throughput alternative to existing methods. Methods: We evaluated proteotyping performance against real-time polymerase chain reaction (PCR) genotyping in a cohort of 104 participants. Plasma samples were analyzed using apoE4 and total apoE assays on the Fujirebio Lumipulse G1200. APOE4 allelic status (non-carrier, heterozygote or homozygote) was determined from the apoE4-to-total apoE ratio. Analytical validation assessed precision, matrix interference and freeze/thaw stability. Results: Proteotyping correctly identified all non-carriers ( n = 53) and all E4/E4 homozygotes ( n = 6). Among 45 heterozygotes, 4 were misclassified as homozygotes, yielding 40% misclassification rate for homozygosity but 100% negative predictive value (NPV). Overall accuracy was 96.2%. The assay performed robustly in the presence of hemolysate and lipemia, with consistent results up to 4 freeze/thaw cycles. Conclusion: Proteotyping reliably rules out E4/E4 homozygosity (100% NPV), enabling rapid eligibility screening for anti-amyloid therapies. Positive homozygosity results require confirmatory testing due to the potential for error. Among non-homozygous results, the assay discriminates E4 carriers from non-carriers, supporting ARIA risk stratification. As plasma phospho-tau217 testing is more commonly used, the ability to run plasma apoE4 testing on the same automated clinical immunoassay analyzer (and the same sample) enables a reflexive testing workflow, supporting more efficient treatment decision-making in the era of disease-modifying therapies.