Transplant Statistics: Annual Report : Appendix B Glossary

This glossary provides descriptions of some of the terms used in the Annual Report. For additional details, please see the Technical Notes in Appendix A.

ABO Blood Type. Includes blood types O, A, B, and AB.

Advisory Committee on Organ Transplantation (ACOT). Formed under the United States. Department of Health and Human Services (HHS) in autumn of 2000, the ACOT was convened in order to strengthen the scientific, medical, and public involvement by HHS oversight of transplantation policy. In particular, ACOT provides independent review and advice to HHS concerning revised organ allocation policies being developed by the nation's transplantation network.

Allocation Policies. Rules or policies, generally based on medical criteria, established by the OPTN to guide and regulate organ allocation or distribution in the United States.

Allograft. An organ transplanted between individuals of the same species.

Annual Death Rate. Specifically identified in this publication as the "annual death rate per 1,000 patient years at risk," it is the number of deaths for every 1,000 patient years on the waiting list. The rate is calculated by dividing the number of patients who died in a given year by the sum of the years (including partial years) that patients spent waiting and then multiplying by 1,000.

Antibody. A protein made by the body's immune system in response to a foreign substance. Exposure to foreign cells from a previous transplant, blood transfusion, or pregnancy may cause a transplant recipient to make antibodies that can react against subsequently transplanted cells, tissues, or organs.

Antigen. A foreign molecule or substance with the capacity to trigger an immune response. Special antigens on the surface of each cell indicate to the immune system whether or not that cell is foreign or native to an individual.

Cadaveric Donor. See Deceased Donor.

Cadaveric Transplant. The transplant of an organ from a deceased donor.

Cardiomyopathy. A disease that causes dysfunction of the heart muscle (myocardium).

Censoring. Used with survival, waiting time before transplant, and time to transplant analyses. Censoring allows the analysis to use all of the follow-up data for a case even if the follow-up period is incomplete. For instance, in the survival analyses, a patient's data are censored when reported as "lost to follow-up."

Centers for Medicare and Medicaid Services (CMS). CMS (formerly the Health Care Financing Administration, or HCFA) is an agency of the United States Department of Health and Human Services (HHS). CMS administers the Medicare and Medicaid programs, which provide health care coverage to America's aged, disabled and indigent populations (about one in every four Americans, including nearly 18 million children), and nursing home coverage for low-income elderly people.

Chimerism. The simultaneous existence and function of components of both the donor's and the recipient's immune systems in the same patient, resulting in cross-regulation of immune system activities.

Cockcroft-Gault Formula. The Cockcroft-Gault Formula calculates an estimate of creatinine clearance, a measure of kidney function, based upon a patient's serum creatinine, age, weight and sex.

Cohort. The observations selected for a study based on a specific time period. For example, in this report the cohort of transplant recipients includes all transplants performed between 1992 and 2001.

Cold Ischemia Time (CIT). The time interval that begins when an organ is cooled with a cold perfusion solution after organ procurement surgery and ends when the organ is implanted.

Compliance. Adherence to protocols or standards. In the context of this report, "compliance" refers to the adherence of OPTN members to the policies and bylaws of the OPTN. Appendix G contains more information on compliance and the role of the OPTN in enforcing compliance.

Confidence Interval. The confidence coefficient is simply the proportion of samples of a given size that may be expected to contain the true mean. That is, for a 95% confidence interval, if many samples are collected and the confidence interval computed, in the long run about 95% of these intervals would contain the true mean.

Creatinine. A waste product of muscle metabolism that is excreted by the kidney. Serum creatinine is an indirect measure of kidney function.

Crossmatch. A test to detect preformed antibodies in a potential recipient's blood against antigens on the surface of a potential donor's cells. A positive crossmatch means that the recipient has antibodies against the donor's cells. With a few exceptions, a positive crossmatch makes successful transplantation between that donor and recipient pair impossible.

Death Rate. The death rate is calculated as the number of patient deaths per 1,000 patient years on the waiting list. The rate is calculated based on the amount of time patients are waiting. Therefore, the smaller the death rate, the smaller the number of deaths per 1,000 patient years waiting.

Deceased Donor. An individual whose tissues or organs are donated after his or her death. Such donations come from two sources: patients who have suffered brain death and patients whose hearts have irreversibly stopped beating. The latter group is referred to as "nonheartbeating donors." Throughout this report, we have used the term "deceased donor" instead of "cadaveric donor."

Division of Transplantation (DoT). The DoT is a component of the Office of Special Programs in the Health Resources and Services Administration (HRSA). The DoT regulates and provides federal oversight and funding support for the nation's organ procurement, allocation, and transplantation system; coordinates national organ and tissue donation activities; funds research to improve donation rates; and administers the National Bone Marrow Registry program.

Donor. An individual who supplies tissue or organs for transplantation.

End-Stage Organ Failure. The permanent need for organ replacement therapy. The option of transplantation exists for the failure of kidney, liver, heart, lung, pancreas, and intestine.

End-Stage Renal Disease (ESRD). Irreversible kidney failure that requires either dialysis or transplantation as renal replacement therapy.

Ethnicity. In this report, race and Hispanic/Latino ethnicity are defined separately, as reported on the data collection forms. Race and ethnicity are not considered mutually exclusive.

Expanded Criteria Donor (ECD). A donor that is not considered to be "ideal" or "standard." Characteristics may include advanced donor age, prior infection with hepatitis B or hepatitis C, hypertension or diabetes mellitus, abnormal donor organ function, and nonheartbeating status of a deceased donor. The term "expanded" is used because an expansion of the donor pool is considered to increase transplantation and is preferred over the term "marginal donor."

Expanded Criteria Donor (ECD) Kidneys. A kidney donated for transplantation from any deceased donor over the age of 60 years; or from a donor over the age of 50 years with two of the following: a history of hypertension, a terminal serum creatinine greater than or equal to 1.5 mg/dl, or death resulting from a cerebral vascular accident (stroke).

FEV₁. The Forced Expiratory Volume in one second (FEV₁) is a measure of lung function. A decline in FEV₁ is associated with worsening lung disease.

Final Rule. The Organ Procurement and Transplantation Network (OPTN) Final Rule (42 CFR Part 121) was issued and published in the Federal Register on April 2, 1998. This rule governs the operation of the OPTN and was amended (resulting from the Institute of Medicine's report, Organ Procurement and Transplantation, 1999). It was issued and published in the Federal Register on October 20, 1999. The Final Rule went into effect on March 16, 2000.

Glomerular Filtration Rate (GFR). The rate at which the blood is filtered by the kidney. The glomerular filtration rate decreases with age and disease.

Graft. In the context of transplantation, a graft is an organ or tissue transplanted from one individual to another of the same species (e.g., human to human).

Graft Survival. Graft survival refers to whether a graft (i.e., an organ) is still functioning at a certain time after transplantation. The time points used in the Annual Report tables include three months, one year, three years, and five years. Ten-year graft survival is also reported in Table 1.14.

Haplotype. One of a pair of three linked tissue-matching genes that are usually inherited as a unit.

Health Resources and Services Administration (HRSA). HRSA, an agency of the United States Department of Health and Human Services, is charged with oversight of the Office of Special Programs, which in turn provides oversight to the Division of Transplantation. The mission of HRSA is to improve the nation's health by assuring equal access to comprehensive, culturally competent, quality health care for all. The goal is to assure total access health care and to eliminate health disparities for all Americans. HRSA supports a nationwide network of 643 community and migrant health centers and 144 primary care programs for the homeless and residents of public housing, serving 8.1 million Americans each year. HRSA also works to build the health care workforce and maintains the National Health Service Corps, oversees the nation's organ transplantation system, helps provide health resources for medically under-served populations, works to decrease infant mortality and improve child health, and provides services to people with AIDS through the Ryan White CARE Act programs. In the fiscal year beginning October 1, 2000, Congress appropriated $6.23 billion to HRSA, including $1.3 billion to provide primary health care in underserved areas, $1.8 billion to care for underserved people with HIV/AIDS, $964 million for services that improve maternal and child health, and $352 million to health professions training and quality assurance.

Heterotopic Transplant. Transplantation of an organ to a site that is different from the location that the organ would ordinarily occupy within the body.

Histocompatibility Antigens. See Human Leukocyte Antigen System (HLA System).

Human Leukocyte Antigen System (HLA System). Human Leukocyte Antigens (HLA), also known as histocompatibility antigens, are molecules found on all nucleated cells in the body. Histocompatibility antigens help the immune system to recognize whether or not a cell is foreign to the body. These antigens are inherited from one's parents. Human leukocyte antigens are used to determine the compatibility of kidneys and pancreata for transplantation from one individual to another. The major groups of HLA antigens are HLA-A, HLA-B, and HLA-DR. The values shown in this report are based on the six HLA antigens (two each for the A, B, and DR loci) reported for both donors and recipients. Tables reporting the level of HLA mismatch indicate the number of HLA antigens found in the donor that are not shared by the recipients. Generally speaking, the smaller the number of HLA mismatches the better the compatibility between donor organ and recipient.

Immunogenicity. The capacity of an antigen to stimulate an immune response.

Immunosuppression. The suppression of the immune response, usually with medications, to prevent the rejection of a transplanted organ or tissue. Medications commonly used to suppress the immune system after transplantation include prednisone, methylprednisolone, azathioprine, mycophenalate mofetil, cyclosporine, tacrolimus, and rapamycin, among others.

Induction Therapy. The administration of a brief course of high-dose immunosuppression in the early posttransplant period. Induction therapy precedes and overlaps with less intense long-term maintenance immunosuppression.

Informed Consent. The process of agreeing to accept a medical test, procedure, or treatment. Informed consent is based on (a) full disclosure of the nature, risks, and benefits of the intended medical intervention; (b) comprehension of the disclosed elements; (c) competence to make an independent decision; and (d) freedom from coercion to allow for a truly voluntary response.

Inotropes. Medications that increase the force of contraction of the heart muscle.

Justice. As applied to the medical ethics of transplantation, justice refers to allocation of organs to those patients in the most immediate need. Issues of justice are balanced by concerns of utility that, in this context, refer to allocating organs to those individuals who will make the "best" use of them. An example would be whether a potential recipient facing imminent death without a transplant but with a poorer chance of long-term survival should be given a transplant in preference to another individual with less immediate risk of death but a better long-term prognosis.

Living Donor. A living person who donates an organ for transplantation, such as a kidney or a segment of the lung, liver, pancreas, or intestine. Living donors may be blood relatives, emotionally related individuals, or altruistic strangers.

Median Time to Transplant. This statistic reports the time at which half of the candidates (median = 50%) will have received a transplant, among all those initially listed. If more than half of candidates are removed or die before receiving a transplant, or if the time is longer than the longest time available for the candidates included in the calculation, then this statistic is not reported. This median time to transplant considers all candidates who are initially registered on the waiting list and is generally longer than the median waiting time. It is useful for candidates at the time they are first put on the waiting list.

Median Waiting Time. This statistic reports the time at which half of the candidates registered on the waiting list would receive a transplant, if they remained active on the waiting list. It is calculated using the successive rates of transplantation seen at each time after registration, among candidates who remain active on the waiting list (dropping candidates when they die or are removed from the waiting list and excluding inactive times). This time is generally shorter than the median time to transplant since it uses transplant rates among those who remain active on the waiting list.

Medical Urgency Status Codes. Each candidate on the liver and heart waiting lists is assigned a status code which corresponds to how medically urgent it is that he or she receives a transplant. Medical urgency status for liver and heart is reported in the waiting list, recipient, and survival tables. Listed below are the definitions for each code, covering the last 10 years.

Medical Urgency Status Codes for Liver Allocation.

Medical Urgency Status Codes for Heart Allocation.

Mismatch. See Human Leukocyte Antigen System (HLA System).

Model for End-Stage Liver Disease (MELD). Uses three laboratory values (bilirubin, creatinine and INR) to calculate a score, on a scale of 6 to 40, that is predictive of the risk of death within three months on the liver waiting list.

National Organ Transplant Act (NOTA). The National Organ Transplant Act (1984 Public Law 98-507), approved October 19, 1984 and amended in 1988 and 1990, provided for the establishment of the Task Force on Organ Transplantation; authorized the Secretary of HHS to make grants for the planning, establishment, and initial operation of qualified OPOs; and established the formation of the Organ Procurement and Transplantation Network (OPTN) and Scientific Registry of Transplant Recipients (SRTR).

Nonheartbeating Donor. See Deceased Donor.

Organ Preservation. Between procurement from a donor and transplantation into a recipient, organs require special methods of preservation. The length of time that organs and tissues can be kept outside the body varies, depending on the organ, the preservation fluid, and the temperature.

Organ Procurement and Transplantation Network (OPTN). Under a contract from HRSA and with oversight from the DoT, the OPTN operates the national network for organ procurement and allocation and works to promote organ donation. Through its policies, the OPTN works to ensure that all patients have a fair chance at receiving the organ they need, regardless of age, sex, race, lifestyle, religion, or financial or social status. The current OPTN contractor is the United Network for Organ Sharing (UNOS), based in Richmond, Virginia.

Organ Procurement Organization (OPO). An organization designated by CMS and responsible for the procurement of organs for transplantation and the promotion of organ donation. There are currently 59 certified OPOs operating in the United States; each is a separate, private, nonprofit organization with its own board of directors.

Panel Reactive Antibody (PRA). The percent PRA value is a measure of a patient's level of sensitization to donor antigens. It is the percentage of cells from a panel of blood donors against which a potential recipient's serum reacts. The PRA reflects the percentage of the general population that a potential recipient makes antibodies (is sensitized) against. The higher the PRA, the more sensitized a patient is to the general donor pool, and thus the more difficult it is to find a suitable donor. A patient may become sensitized as a result of pregnancy, a blood transfusion, or a previous transplant.

Patient Survival. Patient survival refers to whether a transplant recipient is still alive at a certain time after transplantation. The time points used in the Annual Report tables include three months, one year, three years, and five years. Ten-year patient survival is also reported in Table 1.14.

Pediatric End Stage Liver Disease (PELD) Scoring System. Uses three laboratory values (albumin, bilirubin and INR), a presence of growth failure (<2 standard deviations below average height or weight), and an indicator of whether the patient is less than one year of age to calculate a score predictive of the risk of death within three months on the liver waiting list for candidates under the age of 18. The range of PELD scores is greater than that of MELD, ranging from less than zero to greater than 40. 

Percentile. The Nth percentile measure is the value at which N% of the cases are at or below that percentile. For instance, for liver waiting list registrations in 1998, the 25th percentile for waiting time is 140 days. This means that by 140 days after being added to the liver-transplant waiting list, 25% of registrants will have been transplanted. For the same group, the median is 390 days. The median is defined as the 50th percentile. For this group of liver registrants, 50% had been transplanted by 390 days.

Procurement. The process of donor screening and the evaluation, removal, preservation, and distribution of organs, tissues, or cells for transplantation.

Race. In this report, race and ethnicity are defined separately, as reported on the data collection forms. The two are not mutually exclusive. Race includes the following categories:

• White
• African American (listed as Black or African American)
• Asian (listed as Asian, Native Hawaiian, or other Pacific Islander)
• Other (listed as American Indian or Alaskan Native, Mid-East or Arabian, Indian Sub-Continent or multiracial)

Recipient. A transplant patient who receives an organ or tissue transplant.

Rejection. A phenomenon that occurs when the immune system attacks a transplanted organ, tissue, or cell. Immunosuppressive drugs help prevent rejection.

Scientific Registry of Transplant Recipients (SRTR). The SRTR provides analytic support for the ongoing evaluation of the scientific and clinical status of solid organ transplantation in the United States. With oversight and funding from the DoT, the SRTR is currently administered by University Renal Research and Education Association (URREA), in collaboration with the University of Michigan.

Sensitization. Potential recipients are "sensitized" if their immune system makes antibodies against potential donors. Sensitization usually occurs as a consequence of pregnancy, blood transfusions, or previous transplantation. The degree of sensitization is measured by PRA. Highly sensitized patients are more likely to reject an organ transplant than are unsensitized patients.

Standard Error. The standard error me12asures the level of precision associated with the estimate of the mean of a population. Categories that include a large number of transplants generally have small standard errors, while categories with relatively few transplants generally have large standard errors. Survival rates associated with a smaller standard error are more precise than those associated with a larger standard error. Standard errors are presented in the graft and patient survival rates tables.

Thoracic Organs. Organs located in the chest, i.e., the heart and lungs.

Time to Transplant (TT). The time between when a patient is registered on a waiting list and when that patient receives a transplant. Annual Report tables show the median and other percentiles of time to transplant. The median time to transplant is the time by which 50% of a group of registrants have received a transplant. Among the factors affecting time to transplant are the shortage of organs; biologic issues such as blood type, body size of donors and recipients, PRA, immunological factors, and medical urgency status (for liver and heart); donation rates within an area; donation request and consent procedures at OPOs; and patient registration and organ acceptance practices at transplant centers. Table 1.6 presents an alternative measure, "waiting time before transplant," in which inactive time on the waiting list is not counted and patients are censored at any removal from the waiting list.

Tissue Type. An individual's combination of HLA antigens. Matching for tissue type is important in kidney and pancreas transplantation. The tissue type for each patient on the waiting list is entered into a central computer maintained by the OPTN.

Transplant Center. A medical institution within the United States that operates an organ transplant program.

Transplant Program. Components of a transplant center. An individual transplant center may have programs for the transplantation of heart, lung, liver, kidney, pancreas, and/or intestine.

Tumor. An abnormal growth of tissue resulting from an uncontrolled multiplying of cells that serves no physiological function. Tumors can be either malignant (cancerous) or benign (non-cancerous). Malignant tumors include newly developed or "de novo" solid tumors as well as recurrent tumors that had previously been successfully treated. Posttransplant lymphoproliferative disorders (PTLD) are abnormal accumulations of immune cells brought about by the immunosuppression therapies used to reduce organ rejection.

United Network for Organ Sharing (UNOS). Located in Richmond, Virginia, UNOS is a private, nonprofit membership organization that coordinates the nation's transplant system under the OPTN federal contract. UNOS assists the transplant community and the patients it serves by maintaining the national organ transplant waiting list, coordinating the matching and distribution of donated organs, increasing public awareness of the need for donated organs, serving as a forum to create and define organ sharing policies that maximize the use of donated organs, producing professional education tools, and providing extensive information about organ transplantation to patients and the public.

University Renal Research and Education Association (URREA). Located in Ann Arbor, Michigan, URREA is a private, nonprofit organization established for the purpose of collecting information and conducting worldwide epidemiological, clinical, and economic studies of organ failure and related diseases. URREA's mission is to conduct research, to distribute information focused on improving patient care, and to provide analysis and research training opportunities for medical professionals. URREA, in collaboration with the University of Michigan, is responsible for the administration of the Scientific Registry of Transplant Recipients (SRTR).

Utility. As applied to the medical ethics of transplantation, utility refers to allocating organs to those individuals who will make the "best" use of them. Issues of utility are balanced by concerns for justice that, in this context, refer to allocation of organs to those patients in the most immediate need. An example would be whether a potential recipient facing imminent death without a transplant but with a poorer chance of long-term survival should be given a transplant in preference to another individual with less immediate risk of death but a better long-term prognosis.

Ventricular Assist Device (VAD). A mechanical pump that is implanted into a patient with heart failure to maintain blood circulation; it is used as a bridge to heart transplantation.

Waiting List (active, inactive, removal). After evaluation by a team of transplant professionals, a patient is added to the national waiting list by the transplant center. Lists are specific to both geographic area and organ type: kidney, pancreas, kidney-pancreas, liver, intestine, heart, lung, and heart-lung. Each time a donor organ becomes available, a computer generates a list of potential recipients based on factors that may include genetic similarity, organ size, medical urgency, and time on the waiting list. Through this process, a new list that best matches a waiting patient to a donated organ is generated each time an organ becomes available.

1. Active - A patient who does not have any contraindications to transplantation at the current time and is actively awaiting transplantation.
2. Inactive - Patients can be placed on inactive status if they temporarily are not appropriate candidates for transplantation (e.g. an active infection).
3. Removal - A patient can be removed from the waiting list voluntarily, or if he or she becomes too ill to withstand or benefit from transplantation, achieves a spontaneous recovery of organ function, receives a transplant, or dies.

Waiting Time. See Median Waiting Time.