A new study on whether the model used to identify patients most in need of a liver transplant can be improved upon found that measuring serum sodium in potential transplant patients helps to better predict those with a poor prognosis.
The results of this study appear in the March 2005 issue of Liver Transplantation, the official journal of the American Association for the Study of Liver Diseases (AASLD) and the International Liver Transplantation Society (ILTS). The journal is published on behalf of the societies by John Wiley & Sons, Inc. and is available online via Wiley InterScience.
Since 2002, liver allocation in the U.S. has been based on a patient's score on the Model for End-Stage Liver Disease (MELD), which uses levels of three biochemical markers (serum bilirubin, serum creatinine, and prothrombin time expressed as INR) to predict three-month mortality in patients with cirrhosis of the liver listed for transplantation. The current study examined whether factoring serum sodium and hyponatremia (low sodium level in the blood), as additional markers would increase the accuracy of the MELD score to predict risk of death on the waiting list.
Led by Andres E. Ruf, M.D., of the Liver Unit of the Fundacion Favaloro in Buenos Aires, Argentina, the study included 262 patients with cirrhosis who were listed for liver transplantation at Fundacion Favaloro between June 1995 and January 2003. INR, serum bilirubin, creatinine and sodium were measured at the time of listing and used to calculate a MELD score. The efficacy of serum sodium, hyponatremia (defined by serum sodium < 130 mEq/L) and MELD to predict death within 3 and 6 months of listing was analyzed with two different statistical methods. Results of the study showed that when added to the MELD, serum sodium and hyponatremia significantly increased the accuracy of the score in predicting short-term mortality.
"In our study, the prevalence of hyponatremia was significantly higher in patients who died within 3 months (63 percent) than in those who survived 3 months (13 percent)," the authors note. "Similarly, patients with hyponatremia had significantly more advanced liver failure compared to those with normal serum sodium." They add that although hyponatremia ultimately reflects renal impairment, it appears to be a more accurate and early marker of poor outcome than serum creatinine in transplant candidates with advanced cirrhosis.
According to the study, serum sodium, like bilirubin, INR, and creatinine, is an objective, quantitative and reproducible laboratory test, and is therefore a good candidate for inclusion in the mathematical formula of the MELD score. While serum sodium can be decreased with the use of diuretics and can therefore be manipulated, this disadvantage also applies to serum creatinine. The authors conclude that the study "shows that hyponatremia is an excellent predictor of outcome in patients with advanced cirrhosis and significantly increases the efficacy of MELD to predict waitlist mortality."