Lung allocation score
Encyclopedia
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 lung
s 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
.
The LAS system replaces the older method within the United States of allocating donated lungs strictly on a first-come, first-serve 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.
The LAS system is still being evaluated and revised. The reason for this continuing analysis is the need to balance on one hand the desire to help those patients in direst need, versus the statistical likelihood of the patient to survive the procedure, as well as the post-operative risks of infection
and transplant rejection
.
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.
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.
United Network for Organ Sharing
Located in Richmond, Virginia, the United Network for Organ Sharing is a non-profit, scientific and educational organization that administers the only Organ Procurement and Transplantation Network in the United States, established by the U.S. Congress in 1984.UNOS was awarded the initial OPTN...
(UNOS) to assign relative priority for distributing donated lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s for transplantation
Organ transplant
Organ transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...
within the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. 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
Lung transplantation
Lung transplantation, or pulmonary transplantation is a surgical procedure in which a patient's diseased lungs are partially or totally replaced by lungs which come from a donor...
.
The LAS system replaces the older method within the United States of allocating donated lungs strictly on a first-come, first-serve basis, according to blood type
Blood type
A blood type is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells . These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system...
compatibility and distance from the donor hospital. The older method is still used for patients under the age of 12.
The LAS system is still being evaluated and revised. The reason for this continuing analysis is the need to balance on one hand the desire to help those patients in direst need, versus the statistical likelihood of the patient to survive the procedure, as well as the post-operative risks of infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
and transplant rejection
Transplant rejection
Transplant rejection occurs when transplanted tissue is rejected by the recipient's immune system, which destroys the transplanted tissue. Transplant rejection can be lessened by determining the molecular similitude between donor and recipient and by use of immunosuppressant drugs after...
.
Lung allocation scoring method
The lung allocation score is calculated from an a series of formulas that take into account the statistical probability of a patient's survival in the next year without a transplant, how long that survival would be, the probability of survival following 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.Factors in calculating the LAS
There are many factors that are used to calculate the lung allocation score.- diagnosis of the patient (e.g. emphysemaEmphysemaEmphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema, the tissues necessary to support the physical shape and function of the lungs are destroyed. It is included in a group of diseases called chronic obstructive pulmonary...
, cystic fibrosisCystic fibrosisCystic fibrosis is a recessive genetic disease affecting most critically the lungs, and also the pancreas, liver, and intestine...
, etc.); - age of the patient;
- body mass indexBody mass indexThe body mass index , or Quetelet index, is a heuristic proxy for human body fat based on an individual's weight and height. BMI does not actually measure the percentage of body fat. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing...
; - presence or absence of diabetes mellitusDiabetes mellitusDiabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
; - ability to function according to the NYHA scaleNew York Heart Association Functional ClassificationThe New York Heart Association Functional Classification provides a simple way of classifying the extent of heart failure. It places patients in one of four categories based on how much they are limited during physical activity; the limitations/symptoms are in regards to normal breathing and...
; - perecentage of predicted forced vital capacity (FVC);
- systolic pressureCardiac cycleThe cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages...
of the pulmonary arteryPulmonary arteryThe pulmonary arteries carry deoxygenated blood from the heart to the lungs. They are the only arteries that carry deoxygenated blood....
; - meanMeanIn statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....
pressure of the pulmonary artery (only required of sarcoidosisSarcoidosisSarcoidosis , also called sarcoid, Besnier-Boeck disease or Besnier-Boeck-Schaumann disease, is a disease in which abnormal collections of chronic inflammatory cells form as nodules in multiple organs. The cause of sarcoidosis is unknown...
patients); - pulmonary capillary wedge pressurePulmonary capillary wedge pressureThe pulmonary capillary wedge pressure or PCWP is the pressure measured by wedging a pulmonary catheter with an inflated balloon into a small pulmonary arterial branch.Physiologically, distinctions can be drawn among pulmonary venous pressure, pulmonary artery pressure, pulmonary...
(PCW pressure); - flow rate of supplemental oxygenOxygen therapyOxygen therapy is the administration of oxygen as a medical intervention, which can be for a variety of purposes in both chronic and acute patient care...
required at rest; - distance walked in six minutes;
- need or lack of need for continuous mechanical ventilationMechanical ventilationIn medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...
; - levels of creatinineCreatinineCreatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body...
in the blood.
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.
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.
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.- Blood typeBlood typeA blood type is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells . These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system...
compatibility- The blood type of the donor must match that of the recipient due to certain antigenAntigenAn antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
s that are present on donated lungs. A mismatch in blood type can lead to a strong response by the immune systemImmune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
and subsequent rejection of the transplanted organsTransplant rejectionTransplant rejection occurs when transplanted tissue is rejected by the recipient's immune system, which destroys the transplanted tissue. Transplant rejection can be lessened by determining the molecular similitude between donor and recipient and by use of immunosuppressant drugs after...
. In an ideal case, as many of the human leukocyte antigenHuman leukocyte antigenThe human leukocyte antigen system is the name of the major histocompatibility complex in humans. The super locus contains a large number of genes related to immune system function in humans. This group of genes resides on chromosome 6, and encodes cell-surface antigen-presenting proteins and...
s 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.
- The blood type of the donor must match that of the recipient due to certain antigen
- 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 harvesting, ideally both donor and transplant hospitals should be relatively near each other.