Tau is abnormally phosphorylated in the brains of individuals with Alzheimer disease (AD) and serves as a potential target for treatment or intervention.1 However, more research is needed to understand the role of tau in the progression of neurodegenerative disease.2 Examination of tau levels has generally been conducted using cerebrospinal fluid (CSF). This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.