Modifications to the Lung Allocation Score (LAS) system were implemented on February 19, 2015.

Here is an article followed by details of the changes to the LAS system.

New Data Variables

The new LAS calculation is largely based on variables transplant programs already report to the OPTN for lung candidates. Transplant programs can already report cardiac index (CI) and central venous pressure (CVP) to the OPTN for their lung candidates in WaitlistSM. Beginning on February 19, these variables are now factored into the LAS calculation. Additionally, the system allows the entry of CVP data obtained through means other than a heart catheterization.

Total bilirubin (bilirubin) is the only new variable added to the calculation that was not previously collected in the system. Bilirubin is collected and stored serially, like PCO2. You can add the candidate’s current bilirubin value, as well as historical values.

Serum creatinine is also collected and stored serially. Like bilirubin and PCO2, transplant programs can report current and historical values for serum creatinine.

While entry of historic values for the serial data (PCO2, bilirubin, and serum creatinine) is optional, these values may impact a candidate’s LAS.

The New LAS Score System for Lung Transplantation: Insights on a Dynamic Process

In 1990, the Organ Procurement and Transplantation Network (OPTN) began allocating lungs based on blood type and the amount of time a candidate waited on the national wait list. This system did not take into account disease severity or expected benefit after transplantation. Due to the relative shortage of organs, the growing number of patients on the waiting list and the increasing number of deaths during the wait for organs, the necessity of a new lung allocation system became increasingly apparent.

In May 2005, the use of the Lung Allocation Score (LAS) was implemented by the OPTN. The three main objectives included:
Reducing the number of deaths on the lung transplant waiting list
Increasing transplant benefit for lung recipients
Ensuring the efficient and equitable allocation of lungs to active transplant candidates
The LAS system works by assigning a score ranging from 0 to 100 to all candidates older than age 12. It is a weighted combination of the predicted risk of death during the following year on the waiting list and the predicted likelihood of survival during the first year following transplantation.

The implementation of the LAS system resulted in dramatic changes in the allocation process for donor lungs in the United States. It was initiated because the previous system, based on waiting time, failed to accommodate those patients whose health was rapidly deteriorating and who could not tolerate the prolonged waiting times and were therefore more likely to die on the waiting list.

The LAS algorithm attempts to balance wait list urgency with post-transplant survival. Because these data vary among patients with different lung diseases, diagnosis is included as a variable in the LAS calculation. Many recent national studies, including one at UW Hospital and Clinics, demonstrate a marked shift in the number of transplants performed on patients with certain types of lung disease. They show a remarkable increase in transplants performed on patients with idiopathic pulmonary fibrosis, and a decrease in transplants on patients with emphysema. These changes are consistent with the goals of the LAS system, as patients with idiopathic pulmonary fibrosis had a higher mortality on the waiting list under the previous allocation system.

Another important change is that the LAS system caused a significant reduction in the length of time patients wait for transplantation. Patients listed with a very high LAS score have received lungs in as short of time as just a few days. In the previous system, these patients would not even be listed simply because there was no chance organs would become available on time. The average waiting time for lungs was about two years in the previous system.

Based on data provided by the Scientific Registry of Transplant Patients (SRTR), it seems that the use of the LAS system has resulted in fewer deaths on the waiting list. However, it is important to remember that there are patients listed now that would never have been listed before because they had little chance of surviving on the wait list in the old system. These “sick” patients might die on the waiting list in the new LAS system, but would never have been listed in the old system.

In this way, the LAS system might actually inflate death rates. On the other hand, the old system denominator was inflated with relatively healthier emphysema patients that had little chance of being transplanted in the current LAS system. Many of these stable patients stay low on the list simply because their score is not high enough. It is quite likely that these stable patients are not even listed now because they would have a low LAS and placing them on the list to accrue time is no longer advantageous. Consequently, the change in systems not only changes who dies on the wait list, but also who is listed in the first place, thus making a difference in mortality very difficult to interpret.