What is the MELD score and how does it work?

The Model for End-stage Liver Disease (MELD) score was developed in 1994 to assess the risk of a procedure called transjugular portosystemic shunt. Later, the MELD score was evaluated as a tool to rank patients on the liver transplant waiting list and found to be a fair way to assign cadaveric organs to those most in need of transplantation. The MELD score is actually a question that is answered by a mathematical calculation (Table 4): “What is the risk of dying with liver disease in the next 3 months?” In essence, it is a crystal ball with ability to look 3 months into the future. Its accuracy is quite good but, of course, not perfect.

To calculate the MELD score three laboratory tests are necessary: the total bilirubin level, the international normalized ratio (INR), and the creatinine level. Inserting these laboratory values into the MELD formula yields a score between 6 and 40. As shown in Table 4 a score of 6 indicates a 1% chance of dying during the next 3 months and therefore the need for liver transplantation is very small. A MELD score of

40 means there is a 90% chance of death in the next 3 months and transplantation is urgently needed.

The MELD scoring system has been extensively evaluated by the transplant community and is believed to be fair, objective, and unbiased. The MELD score and ranking for liver transplantation do not take into account subjective elements such as quality of life, ability to work, degree of pain, length of time on the waiting list, and number of hospitalizations. In fact, even liver-related complications such as variceal bleeding, ascites, and encephalopathy are not considered in the score. Before the MELD scoring system was approved for ranking candidates on the liver transplant waiting list, it was extensively researched and a computer model was developed based on the experiences of actual patients. The MELD system places all its emphasis on the candidate’s risk of death rather than on his or her quality of life. Compared with the previous ranking system, the MELD system is more effective in preventing death before transplantation. Patients are now more likely to have an opportunity to have life-saving transplantation rather than waiting while the less ill undergo transplantation.

The liver transplant waiting list is actually four lists, separated by blood type: O, A, B, and AB. Within each list patients are prioritized by their MELD scores. When a donor liver becomes available, it is matched with the candidate on the waiting list with the highest MELD score in the identical blood group. A person with a MELD score of 29 is ranked ahead of a person with a MELD score of 25. If the donor is a child, the liver is matched with the highest-ranking pediatric recipient.

The MELD score can be reassessed as often as the patient’s physician believes it is necessary. Any updated information can be used to recalculate and therefore rerank patients on the waiting list. For patients with a MELD score in the range of 6 to 10, new MELD scores must be assessed at least once per year. For scores between 10 and 18, updates every 6 months are necessary. For scores between 18 and 24, new lab data are necessary every month. Scores over 24 require weekly updates.

The UNOS system divides the United States into 11 regions (Figure 7). Organs are procured and distributed within each region. For example, a blood type A liver donated in region 1 goes to the highest-ranking candidate on the blood type A list in region 1. Because of this regional procurement and distribution of organs, each region has its own supply and demand for livers. Regions with a high supply of donor organs and a

small demand are able to transplant candidates with lower MELD scores than regions with low supplies and high demands. This often results in regional inequities in the MELD score needed to appear at the top of the waiting list.

Your position on the waiting list is based exclusively on your MELD score. Movement up (and down) the list is determined by changes in your bilirubin, INR, and creatinine. In the past the amount of time spent waiting on the list was an important factor in your position on the list. Now waiting time is not considered when determining your rank. For this reason your doctors may choose to watch you and follow the progression of your liver disease before listing you for transplantation. The transplant team is aware of the typical score required in each region for transplantation and can evaluate and possibly list you as your score approaches the top of the waiting list.

There are presently no limitations on the number and locations of transplant centers you can be evaluated by and listed with. If you and your doctors believe that your condition would benefit from transplantation earlier than might be provided in your home region, you may seek out transplantation in a region that provides organs to patients with lower MELD scores. Unfortunately, there are numerous drawbacks to evaluation and listing outside your home region: fewer readily available family and friend support systems; necessity to travel for evaluation, transplantation, and frequent office visits; and insurance plans that may not cover out-of-region transplantation expenses.

Another option if you seek to undergo transplantation with a low MELD score may be living donor liver transplantation (discussed in Part 4).

Status 1 is a special designation for patients with fulminant hepatic failure and primary graft nonfunction (PGNF). The risk of death from these two conditions is extremely high. Status 1 patients take priority over the MELD scoring system so that these patients can receive the next available liver from an acceptable blood type–matched donor. In this circumstance patients may receive an identically blood type–matched or a blood type O (universal donor) liver.

Fulminant hepatic failure occurs when a toxin or virus affects a previously healthy person with a normal liver. Examples include acetaminophen toxicity, mushroom poisoning, and rare instances of hepatitis A or hepatitis B. Affected individuals develop jaundice (yellowing of the eyes and skin) followed within 8 weeks by hepatic encephalopathy (confusion caused by the liver’s inability to clear toxins from the blood).

PGNF occurs within 1-2 weeks after liver transplantation. Rarely and for unclear reasons, do some transplanted livers not work properly after surgery. PGNF is not caused by rejection or blocked blood vessels. These patients are usually in critical condition and experience liver failure within 48 hours after transplantation; they require immediate retransplantation.

There is no way to predict how long it takes to move to the top of the transplant waiting list. Because the list is organized by blood group and MELD score, waiting time is no longer relevant in distributing donor organs. Until February 2002, when the MELD scoring system was implemented, waiting time was a critical factor in getting to the top of the list. Simply put, the longer you were on the list, the higher on the list you were placed. The list worked very much like a line to buy movie tickets: If you waited long enough, eventually you got to the ticket window. Because this system allowed people who were not in desperate need to undergo transplantation while terribly ill patients died without the opportunity to receive a donor organ, it was abandoned. Additionally, the candidate’s location on the list depended more on when the referring physician decided to send the patient to the transplant program than on the patient’s actual degree of illness.

The MELD system is based exclusively on the degree of illness and risk of death before transplantation. Waiting time cannot be predicted because receipt of an organ requires deterioration in health, especially in the three critical lab tests: total bilirubin, INR, and creatinine. Primary care physicians, gastroenterologists, and transplant physicians work diligently with their patients to keep them healthy. The goal is to keep patients well enough so that transplantation is a last resort.

Certain UNOS regions in the United States have larger supplies and fewer demands for livers than other regions. The result is variations in waiting times across the country. When the demand is high and the supply of donor livers is low, a person must have a higher MELD score to appear at the top of the list. The score needed to undergo transplantation in such regions is often in the range of 30 to 35. Other regions have large numbers of liver donors, so transplantation can occur at lower MELD scores in the 18 to 20 range. The reasons for the regional differences in donation rates are not clear but may include differences in fatality rates from motor vehicle crashes, access to major hospitals, regional customs and beliefs, and expertise of organ banks in recruiting donors.