Liver Transplant Priorities Better With a Touch of Sodium

Tag : sodium

The effect is relatively modest, Dr. Kim said in a statement, sinceit only makes large changes to the rankings in patients whose MELDscore -- as well as their sodium concentration -- is low.
"In those affected, low sodium has a substantial impact onmortality," he said. "This impact is particularly large in patientswith low MELD, who would be placed low on the waiting list underthe current system."
The MELD formula was developed in 2001 by Mayo Clinic researchersand adopted by the Organ Procurement and Transplantation Network in2002 to rank those waiting for transplant in order of urgency. Itreplaced the earlier Child-Pugh score.
The MELD score is based on three standard tests, total serumbilirubin concentration, indicated by jaundice, the internationalnormalized ratio for the prothrombin time, and serum creatinineconcentration.
Testing for low sodium -- defined in this study as a serum sodiumconcentration between 125 and 140 millimoles per liter -- is alsoreadily available, objective, and reproducible, the researchersnoted.
Using data from the transplant network for 2005 and 2006, Dr. Kimand colleagues evaluated what would have happened had sodiumconcentration been part of the ranking score.
In 2005, there were 6,769 people on the waiting list, including1,781 who got a new liver and 422 who died within 90 days afterregistration. Both the MELD score and the serum sodiumconcentration were significantly associated with mortality: The hazard ratio for death was 1.21 per MELD point (whose valuesrun from six through 40), which was significant at P <0.001. The hazard ratio was 1.05 per one-unit decrease in the serum sodiumconcentration for values between 125 and 140 millimoles per liter,which was also significant at P <0.001.
For most patients -- the 61% who had sodium concentrations above135 millimoles per liter -- the two scores were essentiallyidentical, the researchers said.
The effect of low sodium was also "quite small" for patients whoseMELD score was high, the researchers said, but it could besubstantial in those whose MELD scores were moderate.
For instance, a patient with a MELD score of 10 and a serum sodiumconcentration of 125 millimoles per liter would have a MELDNa scoreof 21 -- a risk of death equivalent to that of a patient with aMELD score of 21 and normal sodium.
When the researchers applied the findings to data from 2006, theyfound that 2,159 patients got a transplant and 477 patients diedwithin 90 days of registration.
For most of those who died -- 363 patients -- the two scores weresimilar, but for 110 (or 23%) the difference "was sufficientlylarge that the priority for liver allocation might have beenaltered if the MELDNa score had been used," the researchers said.
The study is "a benchmark in quantifying the risk of death amongpatients with cirrhosis," according to Andrés Cárdenas, M.D., andPere Ginès, M.D., both of the University of Barcelona.
"If the implementation of this new score could avert 7% of deaths,as the authors estimate, it undoubtedly should be considered as amajor step in refining the MELD score," they wrote in anaccompanying editorial.
But the use of the MELDNa score has some practical limitations,they said, including inter-laboratory variability in sodiummeasurements, which might increase the "already significantvariability" of MELD.
Also, the sodium concentration -- unlike the other factors measuredby MELD -- is less stable and can be affected by such things asadministration of diuretics or intravenous hypotonic fluids, whichmay affect its prognostic value.
They also pointed out that patients with hyponatremia who undergotransplantation are at increased risk for complications such asneurologic problems and for decreased survival.
Therefore, they said, increasing the number of patients withhyponatremia who undergo transplantation could increase the overallrate of death after transplantation.