An accurate blood-based test for preclinical Alzheimer’s disease would revolutionize the clinical diagnosis of dementia and accelerate the development of effective AD treatments. Currently, amyloid PET scans and cerebrospinal fluid biomarkers are used in research, clinical trials and clinical practice to detect brain amyloidosis. Clinical utility of these biomarkers ultimately is limited by their cost, availability and perceived invasiveness. Apolipoprotein E (APOE) is the most significant genetic risk factor for AD and a molecular component of the amyloid plaques that are the hallmark of AD pathology. The current study will assess the diagnostic value of incorporating blood APOE protein measurements into an already high-performing blood-based biomarker assay.