Extreme hyponatremia as a risk factor for early mortality after liver transplantation in the MELD-sodium era

The impact of hyponatremia on waitlist and post-transplant outcomes following the implementation of MELD-Na-based liver allocation remains unclear. We investigated waitlist and postliver transplant (LT) outcomes in patients with hyponatremia before and after implementing MELD-Na-based allocation. Adult patients registered for a primary LT between 2009 and 2021 were identified in the OPTN/UNOS database. Two eras were defined; pre-MELD-Na and post-MELD-Na. Extreme hyponatremia was defined as a serum sodium concentration ≤120 mEq/l. Ninety-day waitlist outcomes and post-LT survival were compared using Fine-Gray proportional hazard and mixed-effects Cox proportional hazard models. A total of 118 487 patients were eligible (n = 64 940: pre-MELD-Na; n = 53 547: post-MELD-Na). In the pre-MELD-Na era, extreme hyponatremia at listing was associated with an increased risk of 90-day waitlist mortality ([ref: 135-145] HR: 3.80; 95% CI: 2.97-4.87; P < 0.001) and higher transplant probability (HR: 1.67; 95% CI: 1.38-2.01; P < 0.001). In the post-MELD-Na era, patients with extreme hyponatremia had a proportionally lower relative risk of waitlist mortality (HR: 2.27; 95% CI 1.60-3.23; P < 0.001) and proportionally higher transplant probability (HR: 2.12; 95% CI 1.76-2.55; P < 0.001) as patients with normal serum sodium levels (135-145). Extreme hyponatremia was associated with a higher risk of 90, 180, and 365-day post-LT survival compared to patients with normal serum sodium levels. With the introduction of MELD-Na-based allocation, waitlist outcomes have improved in patients with extreme hyponatremia but they continue to have worse short-term post-LT survival.