Phosphorylated Tau Levels in Donated Blood

Study Type: Observational (Laboratory-based biomarker study; no human intervention) Study Design: * Model: Cross-sectional * Time Perspective: Prospective * Sample Source: Donated human blood plasma samples obtained through a blood bank * Enrollment: \~250 plasma samples; \~20 plasma samples of AD patients and \~20 plasma samples of normal control participants, where are purchased from BioIVT (Westbury, NY, USA). Official Title: Observational Measurement of pTau217 in Donated Human Plasma Samples Primary Objective: To determine the prevalence of elevated plasma pTau217 levels in donated blood. Secondary Objectives: 1. To compare pTau217 concentrations with total Tau to assess biomarker distribution in donated blood. 2. To generate preliminary data on whether pTau217 screening could be relevant to transfusion safety guidelines. Primary Outcome Measure: * Proportion of blood samples with plasma pTau217 levels exceeding the threshold established in published Alzheimer's disease biomarker studies (measured by nanoneedle biosensor or equivalent immunoassay). * We will also establish the cut off values of pTau217 of plasma based on the data from 20 AD patients and 30 normal control participants. * Time Frame: At single sample collection Secondary Outcome Measures: * Ratio of pTau217 to total Tau across plasma samples * Distribution of pTau217 levels in the donor population Biospecimen Retention: Samples will be analyzed for biomarker levels; aliquots may be stored for future biomarker validation studies. Eligibility Criteria: * Inclusion: De-identified human plasma samples from standard blood bank donations * Exclusion: Samples failing quality control or insufficient volume Study Population: Approximately 250 de-identified donated plasma samples obtained from healthy adult blood donors. Estimated Enrollment: 250 samples