Objective: To describe variability in concussion biomarker concentrations collected from serum in a sample of healthy collegiate athletes, as well as report reliability metrics in a subsample of female athletes. Methods: Observational cohort study - Aβ42, total tau, S100B, UCH-L1, GFAP, MAP2, and CNPase serum concentrations were measured in 415 (61% male, 40% white, age 19.0±1.2 years) non-concussed collegiate athletes without recent exposure to head impacts. Standardized normative distributions are reported for each biomarker. We evaluated main effects (ANOVAs) of sex and race, reporting demographic-specific normative metrics when appropriate. In a subset of 31 female participants, test-retest reliability (Pearson’s r) and reliable change indices (80%, 90%, and 95% confidence intervals) across a 6-12 month interval are reported for Aβ42, total tau, S100B, and UCH-L1. Results: Males exhibited higher UCH-L1 (p<.001, Cohen’s d=0.75) and S100B (p<.001, d=0.56) than females, while females had higher CNPase (p<.001, d=0.46). Regarding race, black participants had higher baseline levels of UCH-L1 (p<.001, d=0.61) and S100B (p<.001, d=1.1) than white participants. Conversely, white participants had higher baseline levels of Aβ42 (p=.005, d=0.28) and CNPase (p<.001, d=0.46). Test-retest reliability was generally poor, ranging from -.02 – 0.40, and Aβ42 significantly increased from Time 1 to Time 2. Conclusion: Healthy collegiate athletes express concussion-related serum biomarkers in variable concentrations. Accounting for demographic factors like sex and race is essential. Evidence suggested poor reliability for serum biomarkers; however, understanding how other factors influence biomarker expression, as well as knowledge of reliable change metrics, may improve clinical interpretation and future study designs.