*Purpose: While we reported that implementation of MELD-Na based liver allocation improved waitlist outcomes in patients with hyponatremia, its impact on post-transplant outcomes in this population has not been fully discussed. This study assessed post-transplant mortality in liver transplantation (LT) patients with pre-transplant hyponatremia and attempted to identify patients with hyponatremia most at risk for poor outcomes.

*Methods: This was a retrospective study that included 75,406 LT patients between 2002-2017. Source of data was the UNOS registry. Survival analysis was conducted using cox proportional regression. Pre-transplant hyponatremia was categorized as: <120 (extreme), 120-124 (severe), 125-29 (moderate), or 130-134 (mild) mmol/L. Remainder were normal (135-145) or hypernatremia (>145). Multivariate analysis included clinically relevant covariates. Subgroup analysis was conducted for patient age and Karnofsky score. Analysis was also separately conducted on patients who received a LT after 01/10/2016, in order to assess the impact of Na <120 on outcomes in the pre MELD-Na period, defined as prior to 01/10/2016, and post MELD-Na period.

*Results: There were 263 patients (0.3%) with extreme hyponatremia (<120). In multivariate analysis, extreme hyponatremia was significantly associated with decreased 1-year survival (HR: 1.54; 95% CI: 1.12-2.12; p=.008 [ref. Na 135-145). Severe, moderate or mild hyponatremia was not associated with worse post-transplant outcomes. Subgroup analysis was conducted in pre and post-MELD-Na periods. There were 223 patients (0.35%) and 40 patients (0.33%) in pre and post-MELD-Na periods, respectively. 1-year survival was not affected by extreme hyponatremia in pre-MELD-Na period (HR: 1.40; 95% CI: 0.98-1.99; P=.06). However, in the post-MELD-Na period, 1-year survival is significantly decreased among patients with extreme hyponatremia (HR: 2.95; 95% CI: 1.39-6.30; p=.005). For patients <60 years old, 1-year survival was significantly decreased in the extreme hyponatremia group (HR: 1.48; 95% Cl: 1.011-2.16; p=.04); however, in patients older than 60 years, significance is lost (HR: 1.58; p=.09). Patients with functional status of 10%, 20%, or 30% at time of transplant were not significantly impacted by extreme hyponatremia, whereas there was a significant association in those with 40-100% (HR: 1.89; CI: 1.25-2.85; p=.003). Among patients with type II DM and extreme hyponatremia, there was significant decrease in survival at both 30 days (HR: 2.99; 95% Cl: 1.10-8.10; p=.03) and 1-year (HR: 2.60; 95% Cl: 1.43-4.72; p=.002).

*Conclusions: Pre-transplant extreme hyponatremia became a significant risk for early post-LT mortalityafter implementation of MELD-Na based allocation. As a result of a higher likelihood of having multiple comorbidities, the impact of hyponatremia may be masked among patients with older age and poor performance status.

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