The United Network for Organ Sharing (UNOS), which operates the nation's transplant distribution network, begins the process next week of shifting over to its new liver prioritization system by eliminating waiting list statuses 2b and 3 and assigning all patients a new MELD score.

The MELD (Model for End-Stage Liver Disease) Score, ranging from 6 (less ill) to 40 (gravely ill), is designed to reflect how urgently a patient needs a transplant during the next three months. It is calculated by a formula based on the results of three routine lab tests: bilirubin, INR (prothrombin time), and creatinine.

A similar system called PELD (Pediatric End-Stage Liver Disease) that uses slightly different criteria will be implemented at the same time for liver transplant candidates under the age of 18.

For status 2b and 3 patients, a MELD or PELD score will be calculated when the new system goes into effect February 27th based on their current lab results. If the score stays the same or goes down during the first year, these patients will retain the time on the waiting list that they have accumulated under the old system.

If the MELD or PELD score goes up, indicating that the patient is in more urgent need of a transplant, only the time on the waiting list at the higher score will be used to break ties when two or more patients with the same blood type have the same score.

Adult status 2a liver patients will have priority over new adult patients listed under the MELD system for 30 days after February 27th. If 2a patients have not received a transplant by March 29th, their MELD score will be calculated at that time and they will be switched over to the new prioriziation system, with credit for 30 days at that score.

The status 1 category will remain in effect for both adult and pediatric liver transplant candidates, and patients in this category will continue to have the highest priority for receiving an organ.

Other sources: UNOS