Abstract： Objective To observe the changes of serum soluble form of triggering receptors expressed on myeloid cell-1 (sTREM-1) level in full-term newborns with infection and to investigate the relationship between serum sTREM-1 and neonatal bacterial infection.Methods Eighty-five full-term newborns admitted to the neonatal ward of Shanghai Children s Hospital of Shanghai Jiaotong University were selected into this study.According to the locations and severity of infection,patients were divided into 3 groups: severe infection group (n = 27),mild infection group (n = 28),non-infection group (n = 30).The samples of infection groups were collected before using antibiotics and within 48 h after infection symptom occurred; others were collected during hospitalization.For the neonates with organ dysfunction in the severe infection group,samples were also collected at the third and seventh day of infection.Serum sTREM-1 was measured by enzyme-linked immunosorbent assay.Analysis of variance was used to compare the difference between groups.Receiver operating characteristic (ROC) curve was used to calculate the sensitivity,specificity,positive and negative predictive value and Youden index.Results (1) Serum sTREM-1 level of severe infection group[(91.2±47.3) pg/ml] was significantly higher than that of mild infection group[(68.8 + 30.4) pg/ml] and non-infection group[(35.5±17.6) pg/ml],respectively (P＜0.05).(2) Serum sTREM-1 level of the survival newborns (n= 17) in the severe infection group was lower than that of dead ones[(73.1±34.9) pg/ml vs (121.6±49.3) pg/ml,t= - 2.995,P = 0.006].(3) For the survival patients,the serum sTREM-1 level decreased in the first week of infection,while that of dead patients increased,the cut-off value was 100.6 pg/ml.(4) Based on the ROC analysis,43.8 pg/ml was selected as the the cut-off value,area under the curve was 0.868,and sensitivity was 85.5%,specificity 80.0%,positive predictive value 0.887,negative predictive value 0.750,Youden index 0.655.Conclusions Serum sTREM-1 level increases in neonatal infection.The change of serum sTREM-1 level in patients with severe infection is correlated to the prognosis.