Living donor liver transplantation (LDLT) is one of the important and effective solutions for the shortage of deceased donor organs, providing life-saving treatment for many patients with end-stage liver disease or hepatic malignancies. However, using small-for-size grafts (SFSG), defined by a graft-to-recipient weight ratio (GRWR) of less than 0.8, remains challenging for transplant surgeons due to the increased risk of complications [1,2]. Traditionally, a GRWR of at least 0.8 has been considered the minimum safe threshold, but recent evidence suggests that smaller grafts can still be successful under specific conditions.

In this issue of the Annals of Liver Transplantation, a notable study investigates the risk factors associated with using SFSGs in LDLT based on the data collected from a single center in Korea. The authors analyze three key risk factors: recipient age of 60 years or older, a MELD (model for end-stage liver disease) score of 15 or higher, and male donor status [3]. The findings indicate that these factors collectively affect graft survival, providing a novel approach for assessing the risks associated with SFSGs. The results are significant and provide valuable insights into patient outcomes. Recipients without any identified risk factors had a graft survival rate of 100% at 5 years even using SFSGs. Those with one risk factor had a survival rate of 72.7%, while recipients with two or more risk factors had a survival rate of 54.5% (p=0.015). These results highlight the need for a careful approach to decision-making when using SFSGs in LDLT.

There are several essential points to consider from this study. First, the study indicates that recipient age remains an important consideration, as older recipients may still pose a higher risk for GRWR <0.8 transplants and careful selection is necessary to ensure optimal outcomes. Second, the risk factors showed consistent effects across different types of grafts. However, the small sample sizes in subgroup analyses suggest that these results should be interpreted cautiously. Third, the study was intended to validate the results of a previously conducted multicentric cohort study in Korea [4]. However, because the authors’ institution is also participating in the formation of Korean national cohort, some of the authors’ single-center data may overlap with data from the previous study, and therefore, it is difficult to assert that this study achieved complete external validation. Finally, it is not always a GRWR <0.8 which results in small-for-size syndrome (SFSS). It is more importantly a state of relative portal hyperperfusion resulting in a cascade of microcirculatory changes [5,6]. Therefore, other various factors apart from graft volume including the degree of recipient’s portal hypertension, graft condition and adequate vascular inflow/outflow can lead to a relative insufficiency of graft size. It is for this reason that portal flow modulation has recently emerged as one of the methods to prevent SFSS. This study did not consider hemodynamic factors due to the limitations of a retrospective study. Additional research including hemodynamic factors appears to be needed in the future.

Nonetheless, these findings hold substantial implications for clinical practice. In evaluating the suitability of LDLT with SFSGs, transplant teams must thoroughly assess the cumulative impact of the identified risk factors. The risk stratification model proposed by the authors is a valuable tool for guiding patient selection and facilitating evidence-based decision-making. The findings of this validation study are an important step in expanding the safe use of SFSGs in LDLT. Integrating these validated risk factors into standardized selection protocols with or without portal vein modulation could help centers worldwide achieve better outcomes with SFSGs with or without portal vein modulation. Most importantly, this evidence-based approach moves us closer to the goal: ensuring the best possible outcomes for recipients.