_ MELD is a scoring system for assessing the severity of chronic liver disease. It was initially developed to predict death within three months of surgery in patients who had undergone a transjugular intrahepatic portosystemic shunt (TIPS) procedure and was subsequently found to be useful in determining prognosis and then prioritizing for receipt of a liver transplant. This score is now used by United Network for Organ Sharing (UNOS) and Eurotransplant for prioritizing allocation of liver transplants instead of the older Child-Turcotte-Pugh (CTP) score.
MELD was originally developed at the Mayo Clinic. At that point it was called the "Mayo End-stage Liver Disease" score.The original version also included a variable based on the underlying etiology (cause) of the liver disease. The score turned out to be predictive of prognosis in chronic liver disease in general and–with some modifications–came to be applied as an objective tool in assigning need for a liver transplant. The etiology turned out to be relatively unimportant and was also regarded as relatively subjective. It was therefore removed from the score.
In general, a donor liver is matched to a potential recipient on the basis of several factors: ABO blood type, body size, degree of medical urgency and MELD score. UNOS uses a computerized database to distribute organs in a fair manner. Recipients are chosen on the basis of medical urgency within each ABO blood group. Waiting time for liver allocation is only a factor when patients have the same MELD score.
In summary, the priority of an individual patient on the UNOS waiting list for a donor liver depends on the following factors:
Local versus distant (donor organs are first offered locally within a given OPO)
ABO blood type (priority is identical > compatible > incompatible ABO blood type)
Body size (the acceptable body range is determined by the transplant surgeon)
Degree of medical urgency as determined by the MELD score (highest priority given to Status 1 patients)
Everyone has a MELD score, even healthy "normal" people. Base MELD score is computed from the results of three blood tests. As the liver starts to fail, the blood test results change thus changing the MELD's base value. Additional adjustments, called "exceptions", to the MELD occur based on additional conditions of the patient. See below for information on exception types. MELD values indicate the patient’s relative expected mortality: the higher the value, the sicker the patient, indicating a shorter potential survivability. MELD scores will go up and down depending on liver condition.
When organs become available, they are evaluated (tested) to see if they are viable and establish the criterion for matching to the pool of patients that have been placed on the waiting list. All patients with matching criteria form an actual list ranked by the patient's current MELD value. The organ becomes available to the patient with the best matching criteria based on rules set by the United Network for Organ Sharing (UNOS).
UNOS is the private, non-profit organization that manages the nation's organ transplant system under contract with the federal government. Some of the rules involve proximity between the candidate recipient and the organ donor as time is a critical factor to successful transplantation. The rules also allow for some leeway in some of the matching criteria depending on the condition of the organ and the MELD of individuals on the candidate donor list.
MELD uses the patient's values for serum bilirubin, serum creatinine, and the international normalized ratio for prothrombin time (INR) to predict survival. It is calculated according to the following formula:
You can do the math yourself or link to an excellentMELD/PELD calculatorprovided by UNOS.
UNOS has made the following modifications to the score:
If the patient has been dialyzed twice within the last 7 days, then the value for serum creatinine used should be 4.0
Any value less than one is given a value of 1 (i.e. if bilirubin is 0.8, a value of 1.0 is used) to prevent the occurrence of scores below 0 (the natural logarithm of 1 is 0, and any value below 1 would yield a negative result)
Patients with a diagnosis of hepatocellular carcinoma (HCC, aka liver cancer) will be assigned a MELD score based on how advanced the cancer is. This staging system is known as the TNM system. T stands for the local extent of the tumor, N stands for the presence or absence of lymph node metastases, and M stands for the presence or absence of distant metastasis (tumor spread to another organ such as the lung in the case of liver cancer).
In interpreting the MELD Score in hospitalized patients, the 3-month mortality is:
40+ — 71.3% mortality
30–39 — 52.6% mortality
20–29 — 19.6% mortality
10–19 — 6.0% mortality
<9 — 1.9% mortality
In June 2009 the OPTN/UNOS Board of Directors approved standardized criteria and MELD/PELD exception scores for patients with the following diagnoses:
hepatopulmonary syndrome
cholangiocarcinoma
cystic fibrosis
familial smyloidosis
primary hyperoxalruia
portopulmonary hypertension
hyponatremia (very low blood sodium)
Patients with hyponatremia usually have worse liver disease than their labs indicate. The moral here is to talk with your doctor if your lab results show real exception to the normal ranges, you may be able to request for exceptions.