Background: Hyponatremia is associated with higher waitlist mortality among end stage liver disease candidates awaiting liver transplantation(LT). However, studies show that such candidates also have higher post-LT mortality and morbidity. We examined the association of serum sodium with LT survival benefit.

Methods: Scientific Registry of Transplant Recipients data were analyzed for adult LT candidates age≥18years waitlisted between January 1, 2005 and December 31, 2009(n=31,416). We excluded Status-1, and censored candidates upon receipt of a living-donor LT or LT with a MELD exception. The effect of serum sodium on survival benefit (comparing pre- and post-LT mortality rates) was assessed by sequential stratification Cox regression. Each LT recipient was matched with candidates active on the waitlist with the same MELD score in the same donation service area. Serum sodium was categorized based on quartiles(Q1:≤134meq/l; Q2-Q3:135-139meq/l; Q4≥140meq/l). The interaction between survival benefit and serum sodium was tested at pre-defined MELD groups (6-8;9-11;12-14;15-17;18-19;20-29;30-39;40). P-values represent the test of equality across sodium quartiles in each MELD group.

Results:

Table-1 shows the survival benefit (covariate-adjusted post- vs. pre-transplant hazard ratio) by MELD group and serum sodium quartiles. LT survival benefit significantly increased as serum sodium decreased for candidates with MELD scores 20-29(p<0.0001), 30-39(p=0.02) and 40(p=0.004). There was no significant interaction between survival benefit and serum sodium at MELD scores<20.

Conclusions: The association between serum sodium and LT survival benefit is limited to candidates with MELD scores≥20. The currently proposed addition of sodium to MELD-based allocation would provide enhanced organ access to lower-MELD candidates with low sodium, despite the absence of a demonstrable survival benefit advantage compared to other lower-MELD patients.

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