The clinical trial is a prospective, controlled study. All subjects were selected from among inpatients who were hospitalized between Sep.2016 and Dec.2018 in the Respiratory ICU, Surgical ICU and Emergency ICU of 6 general hospitals in Beijing. Based on the Sepsis 3.0,the population(500 subjects) selected met the diagnostic criteria. Based on the KDIGO (Nephrol Dial Transplant. 2012) defines AKI as 3 degrees, the subjects were divided into acute renal injury group (AKI group) and non-acute renal injury group (non-AKI group). Approximately 110 healthy volunteers enrolled as control group. Urine samples were collected from day 1 to day 28 in all patient groups (or to the terminal time point of death), serum samples were collected on days 1, 3, 5, 7, 10, and 14 and the samples were collected from healthy subjects on the day of enrollment. Blood was centrifuged at 3,000 rpm for 15 minutes, and urine at 2,000 rpm for 5 minutes. The supernatants were transferred to Eppendorf tubes and stored at -80°C. All the specimens were re-numbered before the experiment. Urine sTREM-1 was measured by a double antibody sandwich ELISA. This study was approved by the Ethics Committee of the CPLA General Hospital (project No.2014-113-02). The following clinical datas were recorded for all patients through the unified database software: (1) basic clinical information: hospital number, gender, age, underlying disease, hospital admission. (2) Daily vital signs after admission: body temperature, blood pressure, heart rate, respiratory rate, 24h urine volume, Glasgow score. (3) APACHE II score and SOFA score: arterial blood gas analysis, blood routine, C-reactive protein, procalcitonin, blood biochemistry (liver function, renal function, brain natriuretic peptide, blood electrolytes) The APACHE II score and the SOFA score were calculated. (4) 28-day outcome (survival or death). Statistical analyses were conducted by SPSS 16.0 (SPSS, Chicago,IL, USA) and a two-tailed P < 0.05 was considered significant.