OBJECTIVES: To compare the diagnostic value of clinical sepsis criteria to novel protein biomarkers in the burn patient. DESIGN: Prospective observational study. SETTING: American Burn Association verified Burn Center ICU. PATIENTS: Burn patients (n = 24) and healthy volunteers (n = 10). INTERVENTIONS: Enrolled burn patients (n = 24) were stratified based on whether or not they met a clinical definition of sepsis. Four separate clinical criteria for sepsis were analyzed for their diagnostic sensitivity and specificity, which were compared to a panel of protein biomarkers. The most significant protein biomarkers were further analyzed via the area under the receiver operating characteristic curves (AUROCs). MEASUREMENTS AND MAIN RESULTS: Of the clinical criteria, SEPSIS-2 criteria led to the highest AUROC (0.781; p < 0.001), followed by the quick Sequential Organ Failure Assessment score (AUROC = 0.670; p = 0.022). Multiplexing revealed a number of inflammatory proteins (complement C5) and matrix metalloproteinases (MMP1, MMP7) that were significantly elevated in septic samples compared with both healthy controls and nonseptic burn samples. Furthermore, three proteins associated with endothelial dysfunction and glycocalyx shedding revealed diagnostic potential. Specifically, syndecan-1, p-selectin, and galectin-1 were all significantly elevated in sepsis, and all resulted in an AUROC greater than 0.7; analyzing the sum of these three markers led to an AUROC of 0.808. CONCLUSIONS: These data reveal several potential biomarkers that may help with sepsis diagnosis in the burn patient. Furthermore, the role of endotheliopathy as a mechanistic etiology for sepsis after burns warrants further investigation.