Background and aims:Acute liver failure (ALF) is associated withsignificant mortality. Failure to identify non-survivors results inpreventable deaths, while misclassifying prospective survivors maylead to unnecessary transplants (LT). Liver-type fatty acid bindingprotein (FABP1) is a 15 kDa protein expressed in hepatocytes. It haspreviously been demonstrated to improve prognostic discriminationin acetaminophen (APAP)-induced ALF but has not been investigatedin other etiologies of ALF. Our primaryaim was too determine if serialFABP1 levels (early; admission or late; day 3–5) are associated with21-day transplant-free survival in non-APAP ALF. Method:FABP1 was measured in serum samples from 384 ALFpatients (n = 88 transplant-free survivors (TFS), n = 296 died/LT∼NTFS) using solid-phase enzyme-linked immunosorbent assay(ELISA) and analysed with US ALFSG registry data.Results:Of 384 patients, etiologies of ALF included autoimmunehepatitis (AIH, n = 125), drug-induced liver injury (DILI, n = 141) andHepatitis B (n = 118). Overall, 177 (46%) ALF patients received LT.Transplant-free survivors (n = 88) were less likely to requiremechanical ventilation (21 vs. 66%), vasopressors (10% vs. 35%) andor have Grade III/IV hepatic encephalopathy (30% vs. 73%, p < 0.0001for all) compared with patients who died/required LT. FABP1 levelswere significantly lower in TFS patients at day 3–5 (TFS 54 vs. NTFS 66 ng/ml; p = 0.049; see Figure) but not admission (TFS 96 vs. NTFS87 ng/ml; p = 0.67). After adjusting for significant covariates,increased FABP1 levels at late time points (day 3–5) were significantlyassociated with worse outcomes (death/LT) in AIH patients (LogFABP1 Odds Ratio (OR) 3.93 (1.50–10.32), P = 0.0055; AUROC 0.89).Increased late FABP1 was associated with worse outcomes in HBV(Log FABP1 OR 1.85 (0.96–3.59), P = 0.068; AUROC 0.82) and DILI (LogFABP1 OR 1.36 (0.97–1.91), P = 0.079; AUROC 0.72), but these werenot statistically significant after adjusting for covariates. Similarly,FABP1 on admission was not significant (adjusted p > 0.15 for allsubgroups). Conclusion:This is the first report of FABP-1 in non-APAP-ALF. Usedin combination with existing prognostic scores, FABP1 may poten-tiallyhelp identify ALF patients with higher recovery potential at latertime points after a period of organ support.