The lung allocation score (LAS) is a numerical value used by the United Network for Organ Sharing (UNOS) to assign relative priority for distributing donated lungs for transplantation within the United States. The lung allocation score takes into account various measures of a patient's health in order to direct donated organs towards the patients who would best benefit from a lung transplant.[citation needed]
The LAS system replaces the older method within the United States of allocating donated lungs strictly on a first-come, first-served basis, according to blood type compatibility and distance from the donor hospital. The older method is still used for patients under the age of 12.[citation needed]
The LAS system is still being evaluated and revised.[1] The reason for this continuing analysis is the need to balance on one hand the desire to help those patients in direct need, versus the statistical likelihood of the patient to survive the procedure, as well as the post-operative risks of infection and transplant rejection.[2]
Lung allocation scoring method
The lung allocation score is calculated from a series of formulas that take into account the statistical probability of a patient's survival in the next year without a transplant, and the projected length of survival post-transplant. A raw allocation score, summarizing all of the above values, is calculated, and finally this score is normalized to obtain the actual LAS, which has a range from 0 to 100. Higher lung allocation scores indicate the patient is more likely to benefit from a lung transplant.
The post-transplant survival measure is one-year survival after transplantation of the lungs. Factors used to predict it include FVC, ventilator use, age, creatinine, NYHA class and diagnosis.[3] It is used for calculation of transplant benefit by subtracting another variable called waitlist urgency measure from it. The final lung allocation score, which is meant to reflect the overall transplant benefit, incorporates this element as well.[4]
Factors in calculating the LAS
There are many factors that are used to calculate the lung allocation score:[citation needed]
UNOS requires that the various medical results must be current, i.e. obtained within the last six months, or the relevant factor is assigned a zero value. Exceptions can be made if a patient is deemed unable to complete a test due to his or her current condition. In such a case, the physician must obtain permission from the UNOS Lung Review Board to submit a reasonable estimate of how the patient would perform.[citation needed]
In certain instances, a physician may petition the UNOS Lung Review Board to modify a patient's assigned LAS if it is felt that a patient's particular circumstances are not adequately represented by the regular LAS calculation system.[citation needed]
How the LAS score is used
The lung allocation score is an important part of the recipient selection process, but other factors are also considered. Patients who are under the age of 12 are still given priority based on how long they have been on the transplant waitlist. The length of time spent on the list is also the deciding factor when multiple patients have the same lung allocation score.[citation needed]
The blood type of the donor must match that of the recipient due to certain antigens that are present on donated lungs. A mismatch in blood type can lead to a strong response by the immune system and subsequent rejection of the transplanted organs. In an ideal case, as many of the human leukocyte antigens as possible would also match between the donor and the recipient, but the desire to find a highly compatible donor organ must be balanced against the patient's immediacy of need.
Age of donor
The donated lung or lungs must be large enough to adequately oxygenate the patient, but small enough to fit within the recipient's chest cavity. Therefore, age is a consideration in the transplant process.
Donor age <12
Donor age 12-17
Donor age 18+
1st priority candidate
age <12
age 12-17
age 18+
2nd priority candidate
age 12-17
age <12
age <12
3rd priority candidate
age 18+
age 18+
Distance from the donor hospital
As donated lungs should be transplanted into the recipient within four to six hours of recovery, ideally both donor and transplant hospitals should be relatively near each other.
Illustrative example
A lung from a 16-year-old donor would first be offered to the person in the age group 12–17 with the highest lung allocation score and matching blood type in the vicinity of the transplant center. If there no suitable recipient in that age group, it would next be offered to the highest LAS-scoring candidate who is under 12 years of age. Finally, it would be offered to the highest LAS-scoring person of age 18 or older. If there is no suitable candidate within the area, the lung may be offered to someone farther away, within certain time and distance constraints.
Notes
^Kern, Dayle: "Advocates at Work: Unique Team Responds to Transplant Inequities for PH Patients", article on page 7 of the Winter 2007 Pathlight newsletter of the Pulmonary Hypertension Association.
^Grady, Denise: "Updated Rules Shorten Waits For New Lungs", article in the September 23, 2006 issue of The New York Times.
