Quantification of plasma APOE4 with a novel automated Lumipulse immunoassay enables the identification of homozygous and heterozygous APOE ε4 carrier status

Introduction: The Apolipoprotein E (APOE) ε4 allele is a significant risk factor for Alzheimer's disease (AD). While genetic testing remains the gold standard for determining APOE status, protein-level quantification could offer advantages in clinical practice. This study evaluates a novel, fully automated immunoassay for quantifying APOE4 and total APOE (Pan-APOE) in plasma samples, assessing its accuracy and clinical utility compared to traditional genetic testing. Materials and methods: Plasma samples from 65 patients (39 ε4 non-carriers, 21 ε4 heterozygous, 5 ε4 homozygous) were analyzed using the Lumipulse 1200 G APOE4 & Pan-APOE immunoassays. The APOE4/Pan-APOE ratio (Ratio%) was calculated to determine ε4 carrier status. Results were compared to genetic testing. Assay repeatability was evaluated using triplicate measurements from three patients with different genotypes. Results: APOE4 and Pan-APOE protein levels and Ratio% differed significantly across ε4 status groups (p < 0.0001). The Ratio% showed no overlap between groups. ROC curve analysis for ε4 carrier identification showed an AUC of 1.00, with 100 % sensitivity and specificity at a 14 % cut-off. Perfect agreement was observed between the immunoassay and genetic testing (Cohen's kappa = 1.00, p < 0.0001). Intra-assay CV was <5 % for APOE4 and <8 % for Ratio%. Discussion: This novel immunoassay demonstrates excellent and potential for faster results could offer advantages in clinical practice, particularly for AD therapy eligibility evaluation. However, further validation in larger, diverse cohorts is necessary before considering widespread clinical implementation.