Prognostic models are useful in estimating disease severity and survival and are used to make decisions regarding specific medical interventions. These models are developed using analytical methods that involve determining the effects of variables of interest (eg, demographic data, clinical data and laboratory values) on specific outcomes such as death.
Several prognostic models are currently used in healthcare settings. Some focus on generalized health status, such as the Acute Physiology and Chronic Health Evaluation System (APACHE III) , while others are disease specific. Examples of the latter include models for predicting survival in patients with primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC), and alcoholic liver disease [2-5]. Two models that are used commonly in the care of patients with chronic liver disease are the Child-Pugh score and the more recently described Model for End-stage Liver Disease (MELD) [6-10].
MELD is a prospectively developed and validated chronic liver disease severity scoring system that uses a patient's laboratory values for serum bilirubin, serum creatinine, and the international normalized ratio for prothrombin time (INR) to predict survival (calculator 1 and calculator 2). In patients with chronic liver disease, an increasing MELD score is associated with increasing severity of hepatic dysfunction and three-month mortality risk . Given its accuracy in predicting short-term survival among patients with end-stage liver disease, MELD has been adopted by the transplant community in the United States for prioritization of patients awaiting liver transplantation. As will be discussed below, the MELD score has been modified slightly since its original development such that the etiology of liver disease is no longer routinely included in the model. Furthermore, revisions to the MELD scoring system have eliminated the possibility of generating negative scores.
The MELD model that is currently used by the United Network for Organ Sharing (UNOS) in prioritizing allocation of deceased donor organs for liver transplantation is calculated according to the following formula:
●MELD = 3.8[Ln serum bilirubin (mg/dL)] + 11.2[Ln INR] + 9.6[Ln serum creatinine (mg/dL)] + 6.4
where Ln is the natural logarithm. For ease of use, several calculators are readily available for calculating the MELD score (calculator 1 and calculator 2) (http://optn.transplant.hrsa.gov/resources/professionalResources.asp?index=8) .