The study by Kamath et al. (2001) introduced the **Model for End-Stage Liver Disease (MELD) score**, a validated tool for predicting short-term mortality in patients with end-stage liver disease (ESLD). The model was initially developed to assess risk in patients undergoing transjugular intrahepatic portosystemic shunt (TIPS) procedures, but it was later adopted as the standard for liver transplantation prioritization. The MELD score is calculated using three objective laboratory values: **serum bilirubin, serum creatinine, and the international normalized ratio (INR) for prothrombin time**. The study demonstrated that higher MELD scores correlate with an increased risk of mortality, making it an effective, evidence-based method to predict survival without transplantation.

Clinically, the MELD score revolutionized liver transplant allocation by replacing the older Child-Pugh classification, which included more subjective criteria. Since 2002, it has been the primary system for organ allocation by the United Network for Organ Sharing (UNOS) in the U.S., ensuring that the sickest patients receive priority for liver transplantation. The score is also used to assess prognosis in cirrhotic patients, guide treatment decisions, and evaluate surgical risks. Its widespread adoption has improved fairness in organ allocation by prioritizing patients based on medical urgency rather than waiting time alone.

The study by **Kim et al. (2008)** explored the impact of **hyponatremia (low serum sodium levels)** on mortality in patients awaiting liver transplantation. The researchers analyzed data from the United Network for Organ Sharing (UNOS) database and found that lower serum sodium levels were independently associated with higher mortality risk, even when controlling for the **Model for End-Stage Liver Disease (MELD) score**. Patients with severe hyponatremia (sodium ≤ 125 mEq/L) had significantly worse survival outcomes compared to those with normal sodium levels. These findings highlighted a critical gap in the MELD scoring system, which did not account for the prognostic significance of hyponatremia.

As a result of this study, the **MELD-Na score** was introduced as an updated liver transplant allocation model, incorporating both **MELD and serum sodium levels** to better predict mortality risk. This modification was crucial in prioritizing patients with both severe liver disease and hyponatremia, who were at a disproportionately higher risk of death while waiting for transplantation. The adoption of MELD-Na improved equity in organ allocation by ensuring that patients with severe hyponatremia were not overlooked due to the limitations of the original MELD formula.

The study by **Kim et al. (2021)** introduced **MELD 3.0**, an updated version of the **Model for End-Stage Liver Disease (MELD) score**, designed to improve the prediction of mortality in patients awaiting liver transplantation. The original MELD score, later modified to **MELD-Na**, effectively prioritized patients based on objective laboratory values (**bilirubin, creatinine, INR, and sodium**). However, limitations remained, particularly for specific populations such as **female patients and those with renal dysfunction**. MELD 3.0 addressed these gaps by incorporating **sex as a variable** (to correct for sex-based differences in serum creatinine), adjusting the impact of sodium, and refining the weight of serum creatinine and bilirubin to enhance accuracy. The study validated MELD 3.0 across multiple large datasets, demonstrating superior mortality prediction compared to previous versions.

The adoption of **MELD 3.0** has important clinical implications, particularly in improving fairness in liver transplant allocation. By correcting for sex-related disparities, **women—who previously had lower creatinine levels and were disadvantaged under MELD-Na—receive a more equitable prioritization**. Additionally, the updated model provides a more accurate assessment of mortality risk for all patients, ensuring that the sickest individuals receive transplants based on the most current and precise prognostic data. This refinement represents a crucial step forward in optimizing organ allocation and reducing waitlist mortality in the modern era.