The Science of End-Stage Liver Disease

The liver is the body's primary chemical processing plant. It is responsible for filtering toxins out of the blood, manufacturing the proteins required for blood to clot, and producing bile to digest food. When a patient develops cirrhosis (severe scarring of the liver from alcohol, hepatitis, or fatty liver disease), these vital functions begin to shut down.

Before the year 2002, prioritizing patients on the liver transplant waiting list was heavily subjective. Patients were ranked largely based on how long they had been waiting. Unfortunately, this meant that critically ill patients who had just been added to the list were dying before patients who were relatively stable but had been waiting longer. To fix this, the medical community adopted the MELD Score.

Why These Four Labs?

The MELD score removes all subjectivity by relying entirely on four objective, mathematical lab values:

• Bilirubin: A yellow pigment formed when old red blood cells break down. The liver is supposed to clear it. If the liver fails, bilirubin builds up, causing the patient's skin and eyes to turn yellow (jaundice). High bilirubin means the liver's filtration system is failing.
• INR (Prothrombin Time): The liver manufactures the proteins (clotting factors) that allow blood to scab and clot. If the liver is failing, it stops making these proteins, causing the blood to become dangerously thin. INR measures how long it takes blood to clot; a high INR means the liver's manufacturing plant has shut down.
• Creatinine: Measures kidney function. In advanced liver disease, massive pressure changes in the circulatory system essentially choke off blood flow to the kidneys (hepatorenal syndrome). When the kidneys fail secondary to the liver, mortality risk skyrockets.
• Sodium (Na): Added to the formula by UNOS in 2016. In advanced cirrhosis, the body begins retaining massive amounts of water (ascites), which dilutes the sodium in the bloodstream (hyponatremia). Severely low sodium is a major red flag for impending mortality.

The Transplant Waiting List

A patient's MELD score directly correlates to their 90-day survival probability. A patient with a MELD of 10 has a 94% chance of surviving the next three months. A patient with a MELD of 40 has less than a 29% chance. Therefore, when a donor liver becomes available in a specific region, it is offered to the compatible patient with the highest MELD score first, ensuring the sickest patients are saved.