The New LAS Score System for Lung Transplantation: Insights on a Dynamic Process
By Nilto DeOliveira, MD, Cardiothoracic Surgeon and Director of Lung Transplantation at UW Hospital and Clinics
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.
In addition, diagnoses of pulmonary fibrosis and pulmonary hypertension are established risk factors for the development of primary graft dysfunction, complications and mortality. If the number of transplants for pulmonary fibrosis is increased, so are the rates of primary graft dysfunction, morbidity and mortality. Therefore, much of the increased morbidity and mortality seen after the introduction of the LAS system is due to the shift in the lung diseases that are being transplanted. Many patients with COPD are becoming older and sicker when they finally move up on the list. It is likely that risk will increase with the shift in patient population.
Multiple national studies have documented that the LAS system is achieving its objectives. The LAS has reduced waiting time and altered the lung diseases being transplanted. Sicker patients who would never have been listed on the old system are being transplanted. SRTR data suggest that the first-year mortality after transplantation rate is worse than previous reports. The risk of death is significantly increased for patients with a higher score, and a higher morbidity and longer ICU stay have been documented by many authors. Patients with high LAS scores offer specific challenges in the operating room and post-operative care. These factors will certainly increase the medical and financial resources required for lung transplantation.
The new LAS system is here to stay. This is a dynamic process still in its early years and more time is necessary to evaluate the results of its implementation. At UW Health, we will continue to focus, as a team, on our ultimate goal: to achieve the best possible results in this fascinating, challenging and extremely rewarding field of surgery.