Asken BM, et al. - In this observational cohort study, researchers characterized variability in concentrations of concussion biomarkers collected from serum in a sample of healthy collegiate athletes and reported reliability metrics in a subsample of female athletes. In 415 nonconcussed collegiate athletes without recent exposure to head impacts, β-amyloid peptide 42 (Aβ42), total tau, S100 calcium binding protein B (S100B), ubiquitin carboxy-terminal hydrolyzing enzyme L1 (UCH-L1), glial fibrillary acidic protein, microtubule associated protein 2, and 2′,3′-cyclic-nucleotide 3′-phosphodiesterase (CNPase) serum concentrations were measured. In variable concentrations, healthy collegiate athletes express concussion-related serum biomarkers. It is essential to take into account demographic factors such as sex and race. Findings indicate that serum biomarkers are poorly reliable. However, understanding how other factors influence biomarker expression and knowledge of reliable change metrics can improve clinical interpretation and future study designs.