The MELD-Na score (Model for End-Stage Liver Disease, incorporating Sodium) is the definitive metric used by transplant networks worldwide to allocate donor livers based on medical urgency.
Predicting Liver Failure Mortality
Prior to the MELD score, liver allocation was heavily based on the Child-Pugh score, which included highly subjective variables like the degree of ascites or encephalopathy (which can vary wildly depending on which doctor examines the patient). The MELD score revolutionized hepatology by using exclusively objective laboratory values: Bilirubin (how well the liver clears toxins), INR (how well the liver synthesizes clotting factors), and Creatinine (a marker of hepatorenal syndrome).
The Addition of Sodium
In 2016, UNOS officially incorporated serum sodium into the calculation. In advanced cirrhosis, the body releases massive amounts of antidiuretic hormone (ADH) to compensate for poor effective blood circulation. This causes the kidneys to retain pure water, diluting the sodium in the blood. Therefore, profound hyponatremia is a harbinger of imminent, severe liver decompensation.
Base MELD(i) &= 0.957 × ln(Cr) \ &\quad + 0.378 × ln(Bili) \ &\quad + 1.120 × ln(INR) \ &\quad + 0.643. MELD \ &\quad -Na = MELD \ &\quad + 1.32 × (137-Na) \ &\quad - [0.033 × MELD × (137-Na)].
Clinical Scoring
The score ranges from 6 to 40.
- A score of 6 represents the lowest risk (normal liver function).
- A score of 40 represents the highest priority, with a 3-month mortality risk often exceeding 70% without a transplant.