Sepsis is one of the most lethal conditions encountered in emergency care, with hospital mortality ranging from 20-40% in septic shock, and 11.5% of patients dying within the first 72 hours of presentation. Early presentations are heterogeneous, rapidly evolving, and often accompanied by nonspecific biomarkers, often leading clinicians to make high stakes decisions before definitive diagnostic information is available. In this critical window, distinguishing between bacterial, viral, or non infectious etiologies determines triage acuity, antimicrobial initiation, and monitoring intensity.

The biomarkers used to anchor these early decisions—C-reactive protein (CRP), procalcitonin (PCT), lactate, and leukocyte count—are physiologically limited. These tools quantify downstream inflammatory byproducts, meaning they may remain normal in early bacterial infection, rise in non infectious conditions, and overlap substantially across bacterial and viral illnesses. These limitations create structural diagnostic uncertainty at first contact.

Misclassification in this window has cascading consequences: delayed antibiotics for bacterial sepsis, unnecessary antimicrobial exposure for viral etiologies, propagation of antimicrobial resistance, and the destabilization of emergency department (ED) workflow through triage distortion, resource misallocation, and safety critical delays. This review synthesizes the biological constraints of current sepsis biomarkers and the operational realities of emergency care, highlighting the need for supplemental diagnostic strategies capable of resolving early diagnostic uncertainty through alternative mechanisms.