The liver allocation system in the US is managed by UNOS (United Network for Organ Sharing), which is a charitable organization under contract with the federal government that creates policies that evaluates the process of organ allocation.
For the purposes of allocating livers, UNOS developed a system to prioritize the allocation of livers to the patients who need them most urgently. The formula that predicts the urgency of a liver transplant in patients ages 12 and over is called MELD (model for End Stage Liver Disease) and PELD (Pediatric End Stage Liver Disease model) for children aged 11 and lower.
MELD looks at four lab tests, which are:
a) Bilirubin (measures how effectively the liver excretes bile)
b) INR (measures the liver’s ability to make clotting factors)
c) Creatinine (a measure of renal function as kidney dysfunction is more prevalent as the liver function declines)
d) Serum sodium (measures severity of portal hypertension)
Once these labs are obtained, they are entered into a statistical formula which then gives a score for that particular patient. Scores range from 6 (less ill) to 40 (gravely ill) and predicts survival of these patients if a liver transplant is not received in the next three months. For example, a MELD score of 38 has a mortality of 80 % and a score of 22 10 % without receiving a liver transplant in the next three months.
The priority exceptions to MELD are for Status 1A and 1B patients.
Status 1A is for patients with acute or fulminant liver failure where survival would not be possible beyond a few hours to days without a transplant.
Status 1B is for sick, chronically ill pediatric patients (less than 18 years).
In 2015, a new UNOS policy regarding patients who have hepatocellular carcinoma (HCC) was implemented. Patients who have HCC will be listed at their calculated MELD scores for the first six months. If they continue to meet criteria at 6 months, MELD candidates will have a score of 28 and PELD candidates will have a score of 34.
MELD scores typically go up or down depending on how well the liver is functioning. Patients with higher MELD scores need to have their blood work done frequently to ensure that they are monitored closely for any deterioration.
Once a donor is available, the patients are prioritized based on:
a) donor’s age
b) medical urgency
c) geographical proximity to the donor
Therefore, the list looks at the status 1A and 1B candidates first, then to:
a) MELD score higher than 35 locally or regionally
b) MELD more than 15 locally or regionally
c) National status 1A or 1B
d) National score higher than 15
e) Others with scores less than 15, local, regional or national
Waiting times are not known to predict the need for a liver very accurately, therefore this criterion is used only if two candidates with identical MELD scores are offered a liver.