The MELD score (Model for End-Stage Liver Disease) is a standardized, objective measure used to assess the severity of chronic liver disease in adults. This numerical scale, ranging from 6 to 40, provides a reliable estimate of a patient’s risk of death within three months without a liver transplant. The higher the score, the greater the medical urgency for a new organ. In the United States, the MELD score is the primary tool utilized by the Organ Procurement and Transplantation Network (OPTN) to prioritize candidates for deceased donor liver transplantation.
Understanding the MELD Score Calculation
The MELD score is calculated using a mathematical formula that incorporates the results of four specific laboratory blood tests. These tests reflect how poorly the liver and associated organs are functioning, which correlates directly with short-term mortality risk.
One component is serum bilirubin, a pigment that the liver normally processes and excretes; high levels indicate the liver is failing to clear waste, leading to jaundice. The International Normalized Ratio (INR) assesses the blood’s ability to clot, reflecting the liver’s impaired production of clotting factors. A higher INR suggests greater liver dysfunction and an increased risk of bleeding.
Another factor is serum creatinine, which measures kidney function, as advanced liver disease often compromises the kidneys. The most recent version, known as MELD-Na, also incorporates serum sodium levels. Low sodium levels (hyponatremia) are frequently observed in severe liver failure and are an independent predictor of higher mortality, refining the score’s accuracy.
The Difference Between Listing and Allocation Thresholds
The question of the minimum MELD score involves a distinction between the score needed for listing and the score required for actual organ allocation. The technical minimum MELD score required for an adult patient to be placed on the national liver transplant waiting list is 6. Patients at this level are considered relatively stable and rarely progress to immediate transplantation based on score alone.
The practical minimum score—the allocation threshold needed to actually receive a deceased donor liver—is significantly higher and constantly fluctuates. This score represents the severity of illness required to attain high priority for a scarce organ offer. Across the country, the median MELD score at the time of transplant often falls in the range of 28 to 35 or higher, illustrating the high medical urgency typically required to receive an organ.
A patient with a MELD score of 6 to 15, for example, is formally listed but will likely wait a very long time, if ever, for a deceased donor liver offer based on that score. The MELD score functions as a dynamic priority system, meaning that only those candidates with the highest scores in a given distribution area are prioritized for immediate organ offers.
MELD Exceptions and Special Medical Circumstances
In some cases, a patient’s calculated MELD score may not accurately reflect their true, high risk of death, leading to the creation of MELD exceptions. These are standardized rules that allow transplant programs to request a higher, standardized “exception score” for patients with specific conditions. The exception score grants them an increased priority on the waiting list that better aligns with their actual mortality risk.
One common condition that qualifies is hepatocellular carcinoma (HCC), which is liver cancer that meets specific size and number criteria. Although these patients might have relatively preserved liver function and a low calculated MELD score, their risk of tumor progression and death is high. Other specific examples include hepatopulmonary syndrome, portopulmonary hypertension, and certain metabolic disorders.
The standard exception score is often set near the median MELD score at transplant (MMaT) within a specific geographic area, often MMaT minus three points, and may increase periodically while the patient remains listed. This mechanism ensures that patients with conditions not fully captured by the MELD formula receive equitable access to transplantation.
How Regional Organ Availability Affects the Score
The actual MELD score needed for a transplant is not uniform across the United States, as it is heavily influenced by regional organ availability and demand. Organ distribution is managed by the OPTN using a system based on acuity circles—concentric geographic zones around the donor hospital. This system prioritizes the sickest patients, but the local supply and demand dynamics dictate the score required for an offer.
If a transplant center is located in an area with a high number of critically ill patients and a low number of organ donations, the median MELD score at transplant will inevitably be very high. Conversely, a region with a higher organ donation rate relative to its patient population may see transplants occurring at lower MELD scores.
This variability means that a MELD score of 30 might be the threshold for transplant in one city, while a patient in another city might require a score of 38 to receive an offer. The acuity circle distribution model was implemented to reduce this historic geographic disparity by broadening the distance organs are offered to the sickest patients first. However, the score required for a transplant remains a dynamic number that is a function of the constant interplay between the number of available organs and the collective medical urgency of all listed candidates in that specific distribution network.