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Background and Aim: While it is currently assumed that liver assessment is only possible during normothermic machine perfusion (NMP), there is uncertainty regarding a reliable and quick prediction of graft injury during ex situ hypothermic oxygenated perfusion (HOPE). We therefore intended to test, in an international liver transplant cohort, recently described mitochondrial injury biomarkers measured during HOPE before liver transplantation., Study Design: Perfusate samples of human livers from 10 centers in 7 countries with HOPE-experience were analyzed for released mitochondrial compounds, i.e. flavin mononucleotide (FMN), NADH, purine derivates and inflammatory markers. Perfusate FMN was correlated with graft loss due to primary non-function or symptomatic non-anastomotic biliary strictures (NAS), and kidney failure, as well as liver injury after transplantation. Livers deemed unsuitable for transplantation served as negative control., Results: We collected 473 perfusate samples of human DCD (n=315) and DBD livers (n=158). Fluorometric assessment of FMN in perfusate was validated by mass spectrometry (R=0.7011,p<0.0001). Graft loss due to primary non-function or cholangiopathy was predicted by perfusate FMN values (c-statistic mass spectrometry 0.8418 (95%CI 0.7466-0.9370,p<0.0001), c-statistic fluorometry 0.7733 (95%CI 0.7006-0.8461,p<0.0001). Perfusate FMN values were also significantly correlated with symptomatic NAS and kidney failure, and superior in prediction of graft loss when compared to conventional scores derived from donor and recipient parameters, such as the donor risk index and the balance of risk score. Mitochondrial FMN values in liver tissues of non-utilized livers were low, and inversely correlated to high perfusate FMN values and purine metabolite release., Conclusions: This first international study validates the predictive value of the mitochondrial co-factor FMN, released from complex I during HOPE, and may therefore contribute to a better risk stratification of injured livers before implantation., Impact and Implications: Analysis of 473 perfusates, collected from 10 international centers during hypothermic oxygenated perfusion (HOPE), revealed that mitochondria derived flavin mononucleotide (FMN) values in perfusate is predictive for graft loss, cholangiopathy, and kidney failure after liver transplantation. This result is of high clinical relevance, as recognition of graft quality is urgently needed to improve the safe utilization of marginal livers. Ex-situ machine perfusion approaches, such as HOPE, are therefore likely to increase the number of useable liver grafts., (Copyright © 2024. Published by Elsevier B.V.)