Evaluation of biologic factors also may help in determining the severity of illness. Cady and coworkers [16] proposed use of the arterial blood lactate level to identify patients with severe illness and to assess the severity of sepsis. The Surviving Sepsis Campaign Management Guidelines Committee [4] , and the American College of Chest Physicians and the Society of Critical Care Medicine Consensus Conference Committee [17] have also proposed guidelines that help to identify those patients who are at greater risk for sepsis. Recent reports from Shapiro [18] and Nguyen [19] and their colleagues have emphasized the importance of lactate clearance in identifying those patients who will respond to treatment and have a favorable outcome. Lactate clearance was shown to be a better prognostic factor than a single lactate determination performed on ED admission [18, 19] . However, a single venous lactate measurement above 4 mmol/l predicted short-term and in-hospital risk for death in patients presenting at the ED with suspected infection [20] , even in those with normal arterial blood pressure [21] . A single lactate dosage is thus a valuable tool that may facilitate early detection of at-risk patients. Plasma procalcitonin may also be valuable in this setting. Procalcitonin is a more specific test than C-reactive protein [22] and interleukin-6, and can help the physician to detect sepsis [23] . Higher levels of procalcitonin are sufficiently specific to identify those septic patients who will develop severe sepsis, but it is not sensitive enough for routine use in ED triage [24] .