In the Emergency Department, the physician's purpose is to rapidly and accurately diagnose the severity of a patient's condition so that proper treatment can be administered. Therefore, this study pays close attention to the association and prognostic value of blood lactate on different disease outcomes by systematically reviewing recently published studies. The search strategy was developed based on searches in the year 2022 for potential publications including original articles, case reports, and reviews using the following web databases google scholar, PubMed, and Science Direct. A total of 25 studies were identified and reviewed extensively to evaluate the link between mortality and serum lactate levels. This literature review presents the strong association of elevated serum lactate levels with the in-hospital mortality rate among emergency department patients. These findings suggest that even a moderately raised lactate level in serum can predict the severe outcome in emergency department patients suffering from different conditions. Therefore, early (at the time of administration of hospital) and periodic serum lactate value determination through different techniques and scores is of need and should become part of routine analyses in emergency department to predict and choose therapies that could benefit critically ill patients.