Objective To investigate the value of liver fatty acid-binding protein(L-FABP)in predicting the severity and short-term prognosis of patients with acute-on-chronic liver failure(ACLF).Methods A total of 149 patients with ACLF were selected from a prospective multicenter cohort assessing the platelet function of ACLF patients,and according to the 28-day prognosis after admission,they were divided into survival group with 97 patients and death group with 52 patients.The patients were analyzed in terms of sex,age,etiology,and blood routine,biochemical parameters,and organ failure status within 24 hours after admission,and the level of L-FABP in urine and blood was measured.The independent-samples t test was used for comparison of normally distributed continuous data between two groups,and the Mann-Whitney U test was used for comparison of non-normally distributed continuous data between two groups;the chi-square test was used for comparison of categorical data between two groups.The Spearman test was used to evaluate the correlation between urinary L-FABP and indicators for liver failure.The receiver operating characteristic(ROC)curve was plotted to assess the value of CLIF-OFs,MELD score,and urinary L-FABP in predicting the short-term prognosis of ACLF patients;the Kaplan-Meier analysis was used to evaluate short-term mortality in the high urinary L-FABP group and the low urinary L-FABP group;the Cox proportional hazards model was used to investigate the association of each factor with the short-term prognosis of ACLF.Results There were significant differences between the two groups in white blood cell count,serum total bilirubin(TBil),international normalized ratio,CLIF-OFs,MELD score,urinary L-FABP level,and the proportion of patients with cerebral failure,liver failure,coagulation failure,renal failure,or respiratory failure(all P<0.05).The Spearman correlation analysis showed that urinary L-FABP was significantly positively correlated with serum TBil(r=0.225,P=0.006).Urinary L-FABP level had an area under the ROC curve of 0.804(95%confidence interval[CI]:0.729-0.865,P<0.001)and a cut-off value of 4.779 μg/dL,with a sensitivity of 73.08%,a specificity of 73.91%,and a Youden index of 0.469 9.The Kaplan-Meier survival analysis showed that compared with the low urinary L-FABP group(urinary L-FABP≤4.779 μg/dL),the high urinary L-FABP group(urinary L-FABP>4.779 μg/dL)had a significantly lower 28-day survival rate(P<0.001).The Cox proportional hazards model analysis showed that serum TBil(hazard ratio[HR]=1.003,95%CI:1.001-1.004,P<0.05),CLIF-OFs(HR=2.283,95%CI:1.814-2.873,P<0.05),and high urinary L-FABP level(HR=4.568,95%CI:2.424-8.608,P<0.05)were independent risk factors for the short-term prognosis of ACLF.Conclusion High urinary L-FABP level can be used as a clinical indicator for predicting the short-term prognosis of ACLF,and further studies with larger sample sizes are needed to evaluate its predictive value.