*Purpose: The shortage of liver grafts results in the prioritization of the sickest patients on the waiting list for liver transplantation. Since 2006, the degree of disease severity in transplant candidates in the Eurotransplant (ET) region is estimated with the Model for End-stage Liver Disease (MELD) score. However, MELD does not account for the worse prognosis associated with hyponatremia. Since the prevalence of cirrhosis is on the rise, better prediction of mortality and improved allocation for liver transplantation are becoming increasingly important. This study researches the potential impact of using MELD-Na instead of MELD for the allocation of livers in the Eurotransplant region.

*Methods: All candidates allocated through MELD with chronic liver disease on the ET liver transplant waiting list between 2007-2018 were included. They were followed from first listing to delisting or until 90 days. The relation between MELD and Na values at listing and 90-day mortality was assessed through a multivariate Cox proportional hazard regression. A reclassification table was constructed of the relevant changes in MELD to MELD-Na score. This allowed an estimation of the lives saved if MELD-Na-based allocation would have been used.

*Results: 5223 patients were included. After 90 days, 21.3% were transplanted, 24.2% were removed and 2.8% had died. Hyponatremia of &lt135, &lt130 and &lt125 mmol/L was found in respectively 28.5%, 8.8% and 2.6% of the listed patients. Between 140 to 125 mmol/L, the MELD-corrected risk of 90-day death increased by threefold (2.9; 95%CI 2.30-3.53; p&lt0.001). The hazard ratio for death was 1.16 (95%CI 1.15-1.17; p&lt0.001) per gained MELD point and 1.08 (95%CI 1.06-1.09; p&lt0.001) per 1-unit Na decrease. The MELD-Na had a c-index of 0.847 (SE 0.007, p&lt0.001). Of the deceased patients, 26.3% would have had a significantly higher chance of transplantation with MELD-Na, which equals to an estimated 4.9% decrease in 90-day waiting list mortality.

*Conclusions: The ET waiting list population has a relatively high prevalence of hyponatremia. For transplant candidates, a low Na increases the risk of 90-day mortality by threefold. If MELD-Na would have been used, 26.3% of the deceased patients could have had a significantly higher chance of transplantation. The 90-day waiting list mortality in our study population could have been lowered by 4.9%. Thus, MELD-Na-based allocation could reduce waiting list mortality for the ET region.

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